FIG. 58.--Astacus fluviatilis.--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.
[Editor's note: illustration is reproduced here approximately twice the size of the woodcut in the book.]
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