Fic. 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 
nauplius form (I) (after Reichenbach, x about 23). bp, blastopore ; ¢, carapace; fg, 
fore-gut involution ; h, heart ; hg, hind-gut involution ; 7b, labrum ; mg, medullary 
groove; 0, optic pit; p, endodermal plug partly filling up the blastopore ; pe, pro- 
ue processes ; ta, abdominal elevation; 2, antennules; 3, antenna 4, man- 
ibles. 
