me* Bl. 





Ai 



A 





Mes. 



E 



Fig. 34 



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

 lobes ; En.p, endoderm plate ; Th.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. Ar, 

 first antenna; Az, second antenna; An, anus; G.op, optic ganglion; Lb, 

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

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

 stomoda^um ; 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 ; S1>g, 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.) 



