Flo. 58 —Aatacus fluviatUis. Surf ace views of the earlier stages in tlie developmrnt of 

 the embryo, from the appearance of the blastopore (A) to the assumption of the 

 nauplius form (P) (after Reichenbaoh, x about 23). bp, blastopore , c, carapace ; fg, 

 fore-gut involution ; h, heart ; *g, hind-gut involution ; Ih, labrum ; mg, medullary 

 groove : o, optic pit ; p, enrlodermal plug partly filling up the blastopore ; ;ic, pio- 

 cephalic processes ; Uiy abdominal elevation ; S, antennules ; S, antenrifp i. man- 

 dilihs. 



