FRONTISPIECE: The Common Crayfish. Astacus fluviatilis, Male.
FIG. 1--Astacus fluviatilis.-- Side view of a male specimen (nat. size):--bg, branchiostegite; cg, cervical groove; r, rostrum; t, telson.--1, eye-stalk; 2, antennule; 3, antenna; 9, external maxillipede; 10, forceps; 14, last ambulatory leg; 17, third abdominal appendage; 20, lateral lobe of the tail-fin, or sixth abdominal appendage; XV, the first; and XX, the last abdominal somite. In this and in succeeding figures the numbers of the somites are given in Roman, those of the appendages in ordinary numerals.
FIG. 2--Astacus fluviatilis.-- Dorsal or tergal views (nat. size). A, male; B, female:-- bcg, branchio-cardiac groove, which marks the boundary between the pericardial and the branchial cavities; cg, cervical groove; these letters are placed on the carapace; r, rostrum; t, t', the two divisions of the telson; 1, eye-stalks; 2, antennules; 3, antennæ; 20, lateral lobes of tail-fin; XV-XX, somites of the abdomen.
FIG. 3--Astacus fluviatilis.-- Ventral or sternal views (nat. size). A, male; B, female:-- a, vent; gg, opening of the green gland; lb, labrum; mt, metastoma or lower lip; od, opening of the oviduct; vd, that of the vas deferens. 1, eye-stalk; 2, antennule; 3, antenna; 4, mandible; 8, second maxillipede; 9, third or external maxillipede; 10, forceps; 11, first leg; 14, fourth leg; 15, 16, 19, 20, first, second, fifth, and sixth abdominal appendages; X, XI, XIV, sterna of the fourth, fifth, and eight thoracic somite; XVI, sternum of the second abdominal somite. In the male, the 9th to the 14th and the 16th to the 19th appendages are removed on the animal's left side: in the female, the antenna (with the exception of the basal joint) and the 5th to the 14th appendages on the animal's right are removed; the eggs also are shown attached to the swimmerets of the left side of the body.
FIG. 4--Astacus fluviatilis.-- In A, the gills, exposed by the removal of the branchiostegite, are seen in their natural position; in B, the podobranchiæ (see p. 75) are removed, and the anterior set of arthrobranchiæ turned downwards (x2): 1, eye-stalk; 2, antennule; 3, antenna; 4, mandible; 6, scaphognathite; 7, first maxillipede, in B the epipodite, to which the line points, is partly removed; 8, second maxillipede; 9, third maxillipede; 10, forceps; 14, fourth ambulatory leg; 15, first abdominal appendage; XV, first, and XVI, second abdominal somite; arb. 8, arb. 9, arb. 13, the posterior arthrobranchiæ of the second and third maxillipededs and of the third ambulatory leg; arb'. 13, the anterior arthrobranchiæ of the third maxillipede and of the third ambulatory leg; pbd. 8, podobranchiæ of the second maxillipede; pbd. 13, that of the third ambulatory leg; plb. 12, plb. 13, the two rudimentary pleurobranchiæ; plb. 14, the functional pleurobranchia; r, rostrum.
FIG. 5--Astacus fluviatilis.-- Dissection from the dorsal side (male). A male specimen, with the roof of the carapace and the terga of the abdominal somites removed to show the viscera (nat. size):--aa, antennary artery; ag, anterior gastric muscles; amm, adductor muscles of the mandibles; cs, cardiac portion of the stomach; gg, green glands; h, heart; hg, hind gut, or large intestine; Lr, liver; oa, opthalmic artery; pg, posterior gastric muscles; saa, superior abdominal artery; t, testis; vd, vas deferens.
FIG. 6--Astacus fluviatilis.-- A longitudinal vertical section of the alimentary canal, with the outline of the body (nat. size):-- a, vent; ag, anterior gastric muscle; bd, entrance of left bile duct; cg, cervical groove; cæ, cæcum; cpv, cardio-pyloric valve; cs, cardiac portion of stomach; the circular area immediately below the end of the line from cs marks the position of the gastrolith of the left side; hg, hind-gut; lb, labrum; lt, lateral tooth of stomach; m, mouth; mg, mid-gut; mt, median tooth; oe, oesophagus; pc, procephalic process; pg, posterior gastric muscle; ps, pyloric portion of stomach; r, annular ridge, marking the commencement of the hind-gut.
FIG. 7--Astacus fluviatilis.-- A Gastrolith or "crab's eye". A gastrolith; A. from above; B, from below; C. from one side (all x 5); D, in vertical section (x 20).
FIG. 8--Astacus fluviatilis.-- Attachment of young to swimmeret of mother. A, two recently hatched crayfish attached to one of the swimmerets of the mother (x 4). pr, protopodite; en, endopodite; and ex, exopodite of the swimmeret; ec, ruptured egg-cases. B, chela of a recently hatched crayfish (x 10).
FIG. 9--Astacus fluviatilis.-- Structure of the stomach. A, the stomach with its outer coat removed, seen from the left side; B, the same viewed from the front, after removal of the anterior wall; C, the ossicles of the gastric mill separated from one another; D, the prepyloric ossicle and median tooth, seen from the right side; E, transverse section of the pyloric region along the line xy in A (all x 2). c, cardiac ossicle; cpv, cardiopyloric valve; lp, lateral pouch; lt, lateral tooth, seen through the wall of the stomach in A; mg, mid-gut; mt, median tooth, seen through the wall of the stomach in A; oes, oesophagus; p, pyloric ossicle; pc, pterocardiac ossicle; pp, prepyloric ossicle; uc, uro-cardiac process; t, convexities on the free surface of its hinder end; v1, median pyloric valve; zc, zygocardiac ossicle.
FIG. 10.--Astacus fluviatilis.-- Longitudinal section of the stomach (x 4), c, cardiac ossicle, cae, caecum; c.p.v., cardio-pyloric valve; cs, cushion-shaped surface; hg, hind-gut; hp, aperture of right bile duct; lp, lateral pouch; lt, lateral teeth; mg, mid-gut; mt, median tooth; oes, oesophagus; p, pyloric ossicle; pc, pterocardiac ossicles; pp, perpyloric ossicle; uc, urocardiac process; v1, median pyloric valve; v2 , lateral pyloric valve; x, position of gastrolith; zc, zygocardiac ossicle.
FIG. 11--Astacus fluviatilis.-- Roof of the stomach, from within. View of the roof of the stomach, the ventral wall of which, and of the mid-gut, is laid open by a longitudinal incision (x 4). On the right side (the left in the figure), the lateral tooth is cut away, as well as the floor of the lateral pouch. The letters have the same signification as in fig. 10.
FIG. 12--Astacus fluviatilis.-- Dissection from the side (male). A dissection of a male specimen from the right side (nat.size). a, anus; aa, antennary artery, cut short; ag, anterior gastric muscles, the right cut away to its insertion; bd, aperture of right bile duct; cm, constrictor muscles of stomach; cae, caecum; cpm, right cardio-pyloric muscle; cs, cardiac portion of stomach; em, extensor muscles of abdomen; fm, flexor muscles of abdomen; ga, gastric artery; gn. 1, supraoesophageal ganglion; gn. 2, sub-oesophageal ganglion; gn. 13, last abdominal ganglion; h, heart; ha, hepatic artery; hg, hind-gut; iaa, inferior abdominal artery; la, right lateral aperture of heart; lr, left liver; mg, mid-gut; oa, opthalmic artery; oe, oesophagus; pg, posterior gastric muscles, the right cut away to its insertion; ps, pyloric portion of stomach; sa, sternal artery; saa, superior abdominal arterty; t, (to the left), telson; t (near the heart), testis; vd, left vas deferens; vd1, aperture of left vas deferens; 2, right antennule; 4, left mandible; 9, left external maxillipede; 10, left forceps; 15, first, 16, second, and 20, sixth abdominal appendages of the left side.
FIG. 13.--Astacus fluviatilis.-- The alimentary canal and livers seen from above (nat. size). bd, bile-duct; cae, caecum; cs, cardiac portion of stomach, the line pointing to the cardiac ossicle; hg, hind-gut; mg, mid-gut; pc, pterocardiac ossicle; ps, pyloric portion of stomach, the line pointing to the pyloric ossicle; r, ridge separating mid-gut from hind-gut; zc, zygocardiac ossicle.
FIG. 14--Astacus fluviatilis.-- The corpuscles of the blood (highly magnified). 1-8 show the changes undergone by a single corpuscle during a quarter of an hour; 9 and 10 are corpuscles killed by magenta, and having the nucleus deeply stained by the coloring matter. n, nucleus.
FIG. 15--Astacus fluviatilis.-- A diagrammatic transverse section of the thorax through the twelfth somite, showing the course of the circulation of the blood ( x 3). arb. 12, the anterior or lower, and arb'. 12, the posterior or upper arthrobranchia of the twelfth somite; av, afferent branchial vessel; bcv, branchio-cardiac vein; bg, branchiostegite; em, extensor muscles of abdomen; ep, epimeral wall of thoracic cavity; ev, efferent branchial vessel; fm, flexor muscles of abdomen; fp, floor of pericardium; gn. 6, fifth thoracic ganglion; h, heart; hg, hind-gut; iaa, inferior abdominal artery, in cross section; la, lateral valvular apertures of heart; lr, liver; mp, indicates the position of the mesophragm by which the sternal canal is bounded laterally; p, pericardial sinus; pdb. 12, podobranchia, and plb. 12, pleurobranchia of the twelfth somite; sa, sternal artery; saa, superior abdominal artery; sc, sternal canal; t, testis; XII., sternum of twelfth somite. The arrows indicate the direction of the blood flow.
FIG. 16.--Astacus fluviatilis.-- The heart ( x 4). A, from above; B, from below; C, from the left side. aa, antennary artery; ac, alae cordis, or fibrous bands connecting the heart with the walls of the pericardial sinus; b, bulbous dilatation at the origin of the sternal artery; ha, hepatic artery; la, lateral valvular apertures; s.a.a., superior abdominal artery; st. a, sternal artery, in B cut off close to its origin.
FIG. 17.--Astacus fluviatilis.-- Structure of the gills. A, one of the podobranchiae from the outer side; B, the same from the inner side; C, one of the arthrobranchia; D, a part of one of the coxopoditic setae; E, extremity of the same seta; F, extremity of a seta from the base of the podobranchiaa; G, hooked seta of the lamina; (A--C, x 3; D--G, highly magnified). b, base of podobranchia; cs, coxopoditic setae; cxp, coxopodite; l, lamina; pl, plume, and st, stem of podobranchia; t, tubercle on the coxopodite, to which the setae are attached.
FIG. 18.--Astacus fluviatilis.-- The green gland. A, the anterior part of the body, with the dorsal portion of the carapace removed to show the position of the green glands; B, the same, with the left side of the carapace removed; C, the green gland removed from the body (all x 2). ag, left anterior gastric muscle; c, circumoesophageal commissures; cs, cardiac portion of stomatch; gg, green gland, exposed in A on the left side by the removal of its sac; ima, intermaxillary or cepalic apodeme; oes, oesophagus seen in transverse section in A, the stomach being removed; s, sac of green gland; x, bristle passed from the aperture in the basal joint of the antenna into the sac.
FIG. 19.--Astacus fluviatilis.-- Muscular tissue. A, a single fibre; transverse diameter 1/110th of an inch; B, a portion of the same more highly magnified; C, a smaller portion still more highly magnified; D and E, the splitting up of a part of fibre into fibrillae; F, the connexion of a nervous with a muscular fibre which has been treated with acetic acid. a, darker, and b, clearer portions of the fibrillae; n, nucleus of sarclomma; nv, nerve fibre; s, sarcolemma; t, tendon; 1--5, successive dark bands answering to the darker portions, a, of each fibrilla.
FIG. 20.--Astacus fluviatilis.-- Muscles of chela. The chela of the forceps, with one side cut away to show, in A, the muscles, in B, the tendons ( x 2). cp, carpopodite; prp, propodite; dp, dactylopodite; m, adductor muscle; m', abductor muscle; t, tendon of adductor muscle; t', tendon of abductor muscle; x, hinge.
FIG. 21.--Astacus fluviatilis.-- Articulation of abdominal somites. Two of the abdominal somites, in vertical section, seen from the inner side, to show x, x, the hinges by which they are articulated with one another ( x 3). The anterior of the two somites is that to the right of the figure.
FIG. 22.--Astacus fluviatilis.-- Muscular system. A longitudinal section of the body to show the principal muscles and their relations to the exoskeleton (nat.size). a, the vent; add.m., adductor muscle of mandible; e.m., extensor, and f.m., flexor muscle of abdomen; oes, oesphagus; pcp, procephalic process; t, t', the two segments of the telson; XV-XX, the abdominal somites; 1--20, the appendages; x, x, hinges between the successive abdominal somites.
FIG. 23.--Astacus fluviatilis-- Nerve fibres. Three nerve fibres, with the connective tissue in which they are embedded. (Magnified about 250 diameters.) n, nuclei.
FIG. 24.--Astacus fluviatilis.-- Nerve ganglia. A, one of the (double) abdominal ganglia, with the nerves connected to it ( x 25); B, a nerve cell or ganglionic corpuscle ( x 250). a, sheath of the nerves; c, sheath of the ganglion; co, co', commissural cords connecting the ganglia with those in front, and those behind them. gl.c. points to the ganglionic corpuscles of the ganglia; n, nerve fibres.
FIG. 25.--Astacus fluviatilis.-- Nervous system. The central nervous system seen from above (nat. size). a, vent; an, antennary nerve; a'n, antennulary nerve; c, circumoesophageal commissures; gn. 1, supraoesophageal ganglion; gn. 2, infraoesophageal ganglion; gn. 6, fifth thoracic ganglion; gn. 7, last thoracic ganglion; gn. 13, last abdominal ganglion; oes, oesophagus in cross section; on, optic nerve; sa, sternal artery in cross section; sgn, stomatogastric nerve.
FIG. 26.--Astacus fluviatilis.-- Olfactory and auditory organs. A, the right antennule seen from the inner side ( x 5); B, a portion of the exopodite enlarged; C, olfactory appendage of the exopodite; a, front view; b, side view ( x 300); a olfactory appendages, au, auditory sace, supposed to be seen through the wall of the basal joint of the antennule; setae; en, endopodite; ex, exopodite; sp, spine of the basal joint.
FIG. 27.--Astacus fluviatilis.-- Auditory sac. A, the auditory sac detached and seen from the outside ( x 15); B, auditory hair ( x 100); C, the distal extremity of the same more highly magnified. a, aperture of sac; as, auditory setae; b, its inner or posterior extremity; n n', nerves; r, ridge.
FIG. 28.--Astacus fluviatilis.-- Structure of eye. A, a vertical section of the eye-stalk ( x 6); B, a small portion of the same, showing the visual apparatus more highly magnified; a, cornea; b, outer dark zone; c, outer white zone; d, middle dark zone; e, inner white zone; f, inner dark zone; cr, crystalline cones; g, optic ganglion; op, optic nerve; sp, striated spindles.
FIG. 29.-- Diagram of eye. Diagram showing the course of rays of light from three points x, y, z, through the nine visual rods (supposed to be empty tubes) A--I of a compound eye; a--i, the nerve fibres connected to the visual rods.
FIG. 30.--Astacus fluviatilis.-- The female reproductive organs ( x 2); ov, ovary; od, oviduct; od', aperture of oviduct.
FIG. 31.--Astacus fluviatilis.-- The male reproductive organs ( x 2); t', testis; vd, vas deferens; vd', aperture of vas deferens.
FIG. 32.--Astacus fluviatilis.-- Structure of ovary. A, a two-thirds grown egg contained in its ovisac (x 50); B, an egg removed from the ovisac ( x 10); C, a portion of the wall of an ovisac with the adjacent poriton of the contained egg, highly magnified; ep, epithelium of ovisac; gs, germinal spots; gv, germinal vesicle; m, membrana propria; v, vitellus; vm, vitelline membrane; w, stalk of ovisac.
FIG. 33.--Astacus fluviatilis.-- Structure of testis. A, a lobule of the testis, showing a, acini, springing from b, the ultimate termination of a duct ( x 50). B, spermatic cells a, with an ordinary globular nucleus n; b, with a spindle-shaped nucleus; c, with two similar nuclei; and d, with a nucleus undergoing division ( x 600).
FIG. 34.--Astacus fluviatilis.-- Spermatozoa. A--D, different stages in the development of a spermatozoon from a seminal cell; E, a mature spermatozoon seen from the side; F, the same view en face (all x 850); G, a diagrammatic vertical section of the same.
FIG. 35.--Astacus fluviatilis.-- The last thoracic sternum in the male and female. The last thoracic sternum, seen from behind, with the proximal ends of the appendages, A, in the male, B, in the female, ( x 3). am, articular membrane; cxp, coxopodite; st XIV, last thoracic sternum, vd, aperture of vas deferens.
FIG. 36.--Astacus fluviatilis.-- Transverse section of abdomen. A transverse section through the nineteenth (fifth abdominal) somite ( x 2). e.m., extensor muscle; f.m., flexor muscles; g.n. 12, the fifth abdominal ganglion; h.g., hind-gut; i.a.a., inferior abdominal artery; s.a.a., superior abdominal artery; pl. XIX, pleura of the somite; st. XIX, its sternum; t. XIX, its tergum; ep. XIX, its epimera; 19, its appendage.
FIG. 37.--Astacus fluviatilis.-- Abdominal appendages. Appendages of the left side of the abdomen ( x 3). A, the posterior face of the first appendage of the male; B, the same of the female; C, posterior, and C', anterior faces of the second appendage of the male; D, the third appendage of the male; E, the same of the female; F, the sixth appendage. a, the rolled plate of the endopodite; b, the jointed extremity of the same; bp, basipodite; cx.p., coxopodite; en.p., endopodite; ex.p., expodite.
FIG. 38.--Astacus fluviatilis.-- Connexion between thorax and abdomen. The mode of connexion between the last thoracic and the first abdominal somites ( x 3). a, L-shaped bar; cpe, carapace; cxp. 14, coxopodite of the last ambulatory leg; plb., place of attachment of the pleurobranchia; st. XV, sternum, and t. XV, tergum of the first abdominal somite.
FIG. 39.--Astacus fluviatilis.-- The cephalothoracic sterna and the endophragmal system ( x 2). A, from beneath; B, from above. a, a', arthrophragms or partitions between the articular cavities for the limbs; c.ap, cephalic apodeme; cf, cervical fold; epn. 1, epimeron of the antennulary somite; h, anterior, and h', posterior horizontal process of endopleurite; lb, labrum, m, mesophragm; mt, metastoma; p, paraphragm; I--XIV, cephalothoracic sterna; 1-14, articular cavities of the cephalothoracic appendages. (The anterior cephalic sterna are bent downwards in A so as to bring them into the same plane with the remaining cephalothoracic sterna; in B these sterna are not shown.)
FIG. 40.--Astacus fluviatilis.-- The opthalmic and antennulary somites ( x 3). I, opthalmic, and II, antennulary sternum; 1, articular surface for eyestalk; 2, for antennule; epm, epimeral plate; pcp, procephalic process; r, base of rostrum; t, tubercle.
FIG. 41.--Astacus fluviatilis.-- The rostrum, seen from the left side.
FIG. 42.--Astacus fluviatilis.-- A segment of the endophragmal system ( x 3). aph, arthrophragm; arth, arthrodial or articular cavity; cxp, coxopodite of the ambulatory leg; enpl, endopleurite; ens, endosternite; epm, epimeron; hp, horizontal process of endopleurite; mph, mesophragm; pph, paraphragm; s, sternum of somite; sc, sternal canal.
FIG. 43.--Astacus fluviatilis.-- Longitudinal section of cephalothorax. Longitudinal section of the anterior part of the cephalothorax ( x 3). I--IX, sterna of first nine cephalothoracic somites; 1, eyestalk; 2, basal joint of antennule; 3, basal joint of antenna; 4, mandible; a, inner division of the masticatory surface of the mandible; a', apophysis of the mandible for muscular attachment; cp, free edge of carapace; e, endosternite; enpl, endopleurite; epm, epimeral plate; l, labrum; m, muscular fibres connecting epimera with interior of carapace; mt, metastoma; pcp, procephalic process.
FIG. 44.--Astacus fluviatilis.-- The third or external maxillipede of the left side ( x 3). e, lamina, and br, branchial filaments of the podobranchia; cxp, coxopodite; cxs, coxopoditic setae; bp, basipodite; ex, exopodite; ip, ischiopodite; mpmeropodite; cp, carpopodite; pp, propodite; dp, dactylopodite.
FIG. 45.--Astacus fluviatilis.-- The first and second maxillipedes. A, the first; B, the second maxillipede of the left side ( x 3); cxp, coxopodite; bp, basipodite; e.br., podobranchia; ep, epipodite; en, endopodite; ex, exopodite; ip, ischiopodite; mpmeropodite; cp, carpopodite; pp, propodite; dp, dactylopodite.
FIG. 46.--Astacus fluviatilis.-- The second ambulatory leg of the left side ( x 3). cxp, coxopodite; bp, basipodite; br, gill; cxs, coxopoditic setae; e, lamina of gill or epipodite; ip, ischiopodite; mpmeropodite; cp, carpopodite; pp, propodite; dp, dactylopodite.
FIG. 47.--Astacus fluviatilis.-- The mandible and maxillæ. A, mandible; B, first maxilla; C, second maxilla of the left side ( x 3); ar, internal and ar', external articular process of the mandible; bp, basipodite; cxp, coxopodite; en, endopodite; p, palp of the mandible; sg, scaphognathite; x, internal process of the first maxilla.
FIG. 48.--Astacus fluviatilis.-- The eye-stalk, antennule, and antenna. A, eye-stalk; B, antennule; C, antenna of the left side ( x 3). a, spine of the basal joint of the antennule; c, corneal surface of the eye; exp, exopodite or squame of the antenna; gg, aperture of the duct of the green gland.
FIG. 49.--Astacus fluviatilis.-- The corpuscles of the blood (highly magnified). 1-8 show the changes undergone by a single corpuscle during a quarter of an hour; n, nucleus; 9 and 10 are corpuscles killed by magenta, and having the nucleus deeply stained by the coloring matter. [Same as Fig. 14.]
FIG. 50.--Astacus fluviatilis.-- Epithelium, from the epidermic layer subjacent to the cuticle, highly magnified. A, in vertical section; B, from the surface. n, nuclei.
FIG. 51.--Astacus fluviatilis.-- Connective tissue; A, second form; B, third form. a, cavities; n, nuclei. Highly magnified.
FIG. 52.--Astacus fluviatilis.-- Muscular tissue. A, a single muscular fibre, transverse diameter 1/110th of an inch; B, a portion of the same more highly magnified; C, a smaller portion treated with alcohol and acetic acid still more highly magnified; D and E, the splitting up of a part of a fibre, treated with picro-carmine, into fibrillae; F, the connection of a nervous with a muscular fibre which has been treated with alcohol and acetic acid. a, darker, and b, clearer portions of the fibrillae; n, nuclei; nv, nerve fibre; s, sarcolemma; t, tendon; 1-5, successive dark granular striae answering to the granular poritons, a, of each fibrilla.
FIG. 53.--Astacus fluviatilis.-- Muscular tissue. A, living muscular fibres very highly magnified; B, a fibrilla treated with solution of sodium chloride; C, a fibrilla treated with strong nitric acid. s, septal lines; sz, septal zones; is, interseptal zones; a, transverse line in the interseptal zone.
FIG. 54.--Astacus fluviatilis.-- Nerve ganglia. A, one of the (double) abdominal ganglia, with the nerves connected with it ( x 25); B, a nerve cell or ganglionic corpuscle ( x 250). a, sheath of the nerves; c, sheath of the ganglion; co, co'. commissural cords connecting the ganglia with those in front, and those behind them. gl.c. points to the ganglionic corpuscles of the ganglia; n, nerve fibres.
FIG. 55.--Astacus fluviatilis.-- Three nerve fibres, with the connective tissue in which they are imbedded (magnified about 250 diameters); n, nuclei.
FIG. 56.--Astacus fluviatilis.-- Cuticular tissue. The structure of the cuticle. A, transverse section of a joint of the forceps ( x 4); s, setae; B, a portion of the same ( x 30); C, a portion of B more highly magnified. a, epiostracum; b, ectostracum; c, endostracum; d, canal of seta; e, canals filled with air; s, seta. D, section of an intersternal membrane of the abdomen, the portion to the right in the natural condition, the remainder pulled apart with needles ( x 20); E, small portion of the same, highly magnified; a, intermediate substance; b, laminae. F, a seta, highly magnified; a and b, joints.
FIG. 57.--Astacus fluviatilis.-- Diagrammatic sections of embryos; partly after Reichenbach, partly original ( x 20). A. An ovum in which the blastoderm is just formed. B. An ovum in which the invagination of the blastoderm to constitute the hypoblast or rudiment of the mid-gut has taken place. (This nearly answers to the stage represented in fig. 58, A.) C. A longitudinal section of an ovum, in which the rudiments of the abdomen, of the hind-gut, and of the fore-gut have appeared. (This nearly answers to the stage represented in fig. 58, E.) D. A similar section of an embryo in nearly the same stage of development as that represented in C, fig. 59. E. An embryo just hatched, in longitudinal section; a, anus; bl. blastoderm; bp, blastopore; e, eye; ep.b., epiblast; fg, fore-gut; fg1, its oesophageal, and fg2, its gastric portion; h, heart; hg, hind-gut; m, mouth; mg, hypoblast, archenteron, or mid-gut; v, yelk. The dotted portions in D and E represent the nervous system.
FIG. 58.--Astacus fluviatilis.-- Earlier stages of development. Surface views of the earlier stages in the development of the embryo, from the appearance of the blastopore (A) to the assumption of the naupluis form (F) (after Reichenbach, x about 23), bp, blastopore, c, carapace; fg, fore-gut involution; h, heart; hg, hind-gut involution; lb, labrum; mg, medullary groove; o, optic pit; p, endodermal plug partly filling up the blastopore; pc, procephalic processes; ta, abdominal elevation; 2, antennules; 3, antennae; 4, mandibles.
FIG. 59.--Astacus fluviatilis.-- Later stages of development. Ventral (A, B, C, F) and lateral (D, E) views of the embryo and successive stages of development (after Rathke, x 15). A is a little more advanced than the embryo represented in fig. 58, F.; D, E, and F are views of the young crayfish when nearly ready to be hatched; in E, the carapace is removed, and the limbs and abdomen are spread out. 1-14, the cepalic and thoracic appendages; ab, abdomen; br, branchiae; c, carapace; ep, epipodite of the first maxillipede; gg, green gland; h, heart; lb, labrum; lr, liver; m, mandibular muscles.
FIG. 60.--Astacus fluviatilis.-- Newly-hatched young ( x 6).
FIG. 61.-- Comparative views of the carapace, third abdominal somite, and telson. A, D, & G, Astacus torrentium; B, E, & H, A. nobilis; C, F, & I, A. nigrescens (nat. size). A-C, Dorsal views of carapace; D-F, side views of third abdominal somites; G-I, Dorsal views of telson. a, b, post-orbital ridge and spines; c, banchio-cardiac grooves inclosing the areola.
FIG. 62.-- Comparative views of the first and second abdominal appendages of the male. A & D, Astacus torrentium; B & E, A. nobilis; C & F, A. nigrescens. A-C, 1st abdominal appendage of the male; D-F, endopodite of second appendage ( x 3). a, anterior, and b, posterior rolled edge; c, d, e, corresponding parts of the appendages in each species; f, rolled plate of endopodite; g, terminal division of endopodite.
FIG. 63. Cambarus Clarkii, male (1/2 nat. size), after Hagen.
FIG. 64.-- Parastacus brasiliensis (1/2 nat. size). From southern Brazil.
FIG. 65.-- Astacoides madagascarensis. (2/3 nat. size). From Madagascar.
FIG. 66.-- Diagram of the morphological relations of the Astacina.
FIG. 67. Homarus vulgaris (1/3 nat. size).
FIG. 68. Podobranchiæ of A, Parastacus; B,Nephrops; C, Palæmon. A', C', transverse sections of A and C respectively.a, point of attachment;al, wing-like expansion of the stem;b, base; br, branchial filaments;ep, epipodite;l, branchial laminæ; pl, plume;st, stem.
FIG. 69. Nephrops norvegicus (1/2 nat. size).
FIG. 70. Palinurus vulgaris (about 1/4 nat. size).
FIG. 71. Palæmon jamaicensis (about 5/7 nat. size). A, female; B, fifth thoracic appendage of male.
FIG. 72. Cancer pagurus, male (1/3 nat. size). A, dorsal view, with the abdomen extended; B, front view of "face." as, antennary sternum;or, orbit;r, rostrum; 1. eyestalk; 2. antennule; 3. base of antenna; 3, free portion of antenna.
FIG. 73. Penæus semisulcatus. A, adult (after de Haan, 1/2 nat. size); B, Zoæa, and C, less advanced Zoæa of a species of Penæus.D, Nauplius. (B, C, and D, after Fritz Müller.)
FIG. 74. Cancer pagurus. Development. A, newly hatched Zoæa; B, more advanced Zoæa; C, dorsal, and D, side view of Megalopa (after Spence Bate). (The figures A and B are more magnified than C and D.)
FIG. 75.-- Astacus leptodactylus (after Rathke, 1/3 nat. size).
FIG. 76.-- Australian Crayfish (1/3 nat. size). [note]
[note] The nomenclature of the Australian crayfishes requires thorough revision. I, therefore, for the present, assign no name to this crayfish. It is probably identical with the A. nobilisof Dana and theA. acmatusof Von Martens.
FIG 77.-- MAP OF THE WORLD, showing the geographical distribution of the Crayfishes. I. Eur-asiatic Crayfishes; II. Amurland Crayfishes; III. Japanese Crayfishes; IV. Western North American Crayfishes; V. Eastern North American Crayfishes; VI. Brazilian Crayfishes; VII. Chilian Crayfishes; VIII. Novozelanian Crayfishes; IX. Fijian Crayfishes; X. Tasmanian Crayfishes; XI. Australian Crayfishes; XII. Mascarene Crayfishes.
FIG. 78.-- Cambarus. Walking leg. Cambarus(Guatemala) penultimate leg.cxp, coxopodite; cx.s, coxopoditic setæ; pdb, podobranchia;bp, basipodite;ip, ischiopodite; mp, meropodite;cp, carpopodite;pp, propodite;dp, dactylopodite.
FIG. 79. Palæmon jamaicensis (about 5/7 nat. size). A, female; B, fifth thoracic appendage of male.
FIG. 80.-- A,Pseudastacus pustulosus (nat. size). B,Eryma modestiformis ( x 2). Both figures are after Oppel.
FIG. 81.-- Hoploparia longimana (2/3 nat. size).--cp, carapace;r, rostrum; T, telson; XV., XVI., first and second abdominal somites; 10, forceps; 20, last abdominal appendage.
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