F 



Fig. 34 



A. Ventral view of an egg of Astacus in an early stage of development, cp, optic 

 lobes ; En.p, endoderm plate ; Tk.ab, thoraco-abdominal plate. B. Sagittal 

 section through a slightly older egg. Bl, blastopore ; EC, epiblast ; En, hypo- 

 blast ; mes, mesoblast. C. Ventral view of the so-called nauplius stage. Ai, 

 first antenna; As, second antenna; An, anus; G.op, optic ganglion; L6, 

 labrum ; Md, mandible. D. Sagittal section through an embryo of nearly the 

 same age as C. Ettt, enteron ; Prc, proctodaeum ; st, commencement of the 

 stomodaeum ; other letters as before. E, Ventral view of a more advanced 

 embryo; the thoraco-abdominal rudiment. Th.ab, is well developed and turned 

 forwards ; E, eyes. F. Sagittal section through an embryo of the same age as E. 

 Ht, heart ; Spg, supraoesophageal ganglion ; other lettering as before. It should 

 be noticed that the yolk has been entirely absorbed by the hypoblast cells 

 lining the enteron, so that the latter resemble the yolk-pyramids of the earlier 

 stage, shown in fig. 33, C. (All the figures after Reichenbach.) 



