Fio. 58—^1 /crews fluviatllis. —Surfaca views of the earlier stages in the developninit of 

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

 iiaiiplius form (F) (after Reichenbach, x about 23). hp, blastojiore , c, carapace ; fg, 

 fore-gyt involution ; h, heart ; hg, hind-g\it involution ; Ih, labrum ; mg, medullary 

 groove ; o, optic pit ; jt, en<lodermal plug partly filling up the blastopore ; pc, pro- 

 cephalic processes ; ta, abdominal elevation; 2, antennules ; 3, antennae >4, man- 

 dibles. 



