PLATE II. 



Fig. 14.— Optical section of an old blastula. (From life.) J Ob. X 8 Oc. Camera. X 360. 



Fig. 14a. — Section through an old blastula showing endodermal bodies in blastoccele. y'rr Oil Immersion. X 8 Oc. 



Camera. X 704. 

 Fig. 15. — Longitudinal section through older blaatula than that of tig. 14a showing proliferation of endoderm cells. 



y 1 . Oil Immersion, x 8 Oc. Camera, x 704. 

 Fig. 15a. — Transverse section through a gastrula which is just beginning to gastrulate. Taken through ganglionic 



thickening. ^ Oil Immersion. X 8 Oc. Camera. X 704. 

 Fig. 156. — Transverse section through same specimen as that of rig. 15a. Taken through the middle of the gastrula. 



T 'j Oil Immersion. X 8 Oc. Camera. X 704. 

 Fig. 16. — Longitudinal section through a gastrula which has begun to elongate. fa Oil Immersion. X8 Oc. 



Camera. X 704. 

 Fig. 16a. — Transverse section through anterior end of a gastrula which was a little younger than that of tig. 16. 



Taken just back of the ganglion, ,'j Oil Immersion. X 8 Oc. Camera. X 704. 

 Fig. 166. — Transverse section through same specimen as that of tig. 16a. Taken just in front of anterior end of the 



archenieron. Shows mesoderm arising from the latter. T V Oil Immersion. X 8 Oc. Camera. X 704. 



Fig. 16c. — Continuation of above series. Taken through anterior part of archenteron. T 'j Oil Immersion, x 8 



Oc. Camera. X 704. 

 Fig. 16d. — Continuation of above series. Taken through middle of archenteron. ,V Oil Immersion. X8 Oc. 



Camera. X 704. 

 Fig. 16e. — Continuation of above series. Taken through posterior part of archenteron. j\ Oil Immersion. 



X 8 Oc. Camera. X 704. 

 Fig. 16/. — Continuation of above series. Taken through the region where the lips of the blastopore are closing up. 



yV Oil Immersion. X 8 Oc. Camera. X 704. 

 Fig. 16g. — Horizontal section through a gastrula of the same age as that of tig. 16. T \ Oil Immersion. X8 Oc. 



Camera. X 704. 

 Fig. 17. — Transverse section through a gastrula showing peculiar granular cells arising from the endoderm. T l j Oil 



Immersion. X 8 Oc. Camera. X 704. 

 118 



