Flo. 58. Astacus ftuviatilis. Surface views of the earlier stages in tlie development of 

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

 nauplins iorm (F) (after Reichenbach, x about 23). t'p, blast o] ore , <; carapace ; fg, 

 fore-gut involution ; h, heart ; hg, hind-put involution ; lb, labnim ; mg, medullary 

 groove : o, optic pit ; p, endodermal plug partly firing ->\]i the blastopore ; pc, pio- 

 cephalic j)roceKses ; ta, abdominal elevation ; %, antennules ; 3 antennae k, mau- 



