Flo. 58 —A tciffiis fiuviatilis. — 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 (F) (after Beichenbaeh, x about 23). bp, "blastopore ; c, carapace ; fg, 

 fore-gut involution ; ft, heart : hg t hind-gut involution ; lb, labrum ; mg, medullary 

 groove ; o, optic pit ; p, endodermal plug partly filling up the blastopore ; pc, pio- 

 cephalic processes ; ta, abdominal elevation; 2, antennules ; 3, antennae h, man- 

 dibles. 



