





Fig. 5S.—Astacus fliiviatilis.— Surface views of the earlier stages in the development of 

 the embryo, from tlie ap]iearance of the lilastopore (A) to the assum]ition of the 

 nauplius "fonn (F) (after Reichenbaoh, x about 2;i). hp, blastopore , c, carapaee : fg, 

 fore-gut involution ; h, heart ; /(?, hind-gut involution ; Ih, labmm ; mg, medullary 

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

 cephalic processes ; ta, abdominal elevation ; 2, antennules ; 3, antennse i,, man- 

 dibUs. 



i 



