ANATOMY AND DEVELOPMENT 



embryo has apparently about thirteen somites, which are still 

 quite distinct from one another, and apparently do not com- 

 municate at this stage with the mesenteron. 



The epiblast lying immediately over the somites is, as in the 

 earlier stages, thickened, and the thickenings of the two sides 

 join each other in front of the embryonic mouth, where the 

 anterior pair of mesoblastic somites (the praeoral lobes) are 

 almost in contact. 



The median ventral epiblast, i.e. the epiblast in the area, 

 bounded by the embryonic mouth and anus before and behind 

 and by the developing nerve-cords laterally, is extremely thin, 

 and consists of one layer of very flat cells. Over the dorsal 

 surface of the body the epiblast cells are cubical, and arranged 

 in one layer. 



Measurements of Embryo of Stage E. 



Length of embryo 1*12 mm. 



Greatest width . '64 



Distance from front end of embryonic mouth to hind 



end of embryonic anus ...... '48 



Greatest length of embryonic mouth . . . . '16 



Length between hind end of embryonic mouth and 



front end of embryonic anus ..... '29 



These measurements were made with a micrometer eyepiece, 

 with the embryo lying on its back in the position of fig. 38, so 

 that they simply indicate the length of the straight line connect- 

 ing the respective points. 



This is the last embryo of our series of young stages. The 

 next and oldest embryo was 3'2 mm. in length. It had ringed 

 antennae, seventeen (?) pairs of legs, and was completely doubled 

 upon itself, as in Moseley's figure. 



The pits into the cerebral ganglia and a mouth and anus 

 were present. There can be no doubt that the mouth and anus 

 of this embryo become the mouth and anus of the adult. 



The important question as to the connection between the 

 adult mouth and anus, and the embryonic mouth and anus of 

 the Stage E, must, considering the great gap between Stage E 

 and the next oldest embryo, be left open. Meanwhile, we may 

 point out that the embryonic mouth of Stage E has exactly the 



