mes SI 



A 



-Efi.j}. 



.v\;wv:."-.'';v-;=;.'.'---' (^-op- 



r-i-'ii^i^ftiliiS^i:;;'/'?;/ 





Fig. 34 



A. Ventral view of an egg of Astacus in an early stage of development, c^, 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 ; 77ies, mesoblast. C. Ventral view of the so-called nauplius stage. Ai, 

 first antenna; A2y 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 Ent, enteron; Pre, proctodseum ; j/, commencement of the 



^^ stomodzeum ; other letters as before. E. Ventral view of a more advanced 

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

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

 Hiy heart ; Spg, supracesophageal 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, CP/^f/teflSfei^^iSr^^^flSfeichenbach.) 



