38 AKT. 11. — fi. HATÏA. 



Plate I. 



Surface views of the ova undergoing the process of gastrulation. The 

 figures were all drawn by the author from living specimens. The 

 magnification is about x 30 for all the figures. 



Fit/. 1 — An old morula. The upper translucent part (a.h.) is the anima 

 hemisphere ; the lower opaque part (vJi.) is the vegetative 

 hemisphere. 



Fi(j. 2 — A fully grown morula. The animal hemisphere (a.h.) has become 

 much larger than that in the stage of Fù/. 1, while the vegetative 

 hemisphere (v.h.) is rather reduced in extent. 



Fig. 3a — Side view of a little further advanced ovum. The conical 

 eminence (c.em.) appears as a rounded elevation. The boundary 

 groove (b.g.) has come into view. 



Fig. 'M) — Dorsal view of the same ovum. The proportion of the extent 

 of the animal and vegetative hemispheres is well seen ; the latter 

 is about ^ of the former in bulk. 



Fig. 4« — Side view of a little further developed ovum. The conical emi- 

 nence (c.em.) has become prominent, and a part of the vegetative 

 hemisphere below the eminence has flattened (.,;;;..). The boundary 

 groove (b.g.) has become deeper and is extended farther ventrally. 



Fig. 46 — Dorsal view of the same ovum. A comparison of this with 

 Fig. 3b shows that the part giving rise to the conical eminence 

 is strongly compressed from side to side. 



Fig. 5« — Side view of an ovum in which the gastrula invagination has just 

 begun (bjj.) ; the boundary groove {b.g.) has extended itself far- 

 ther ventrally. 



Fig. :V> — Dorsal view ot the same ovum. The blastopore (bj).) is seen like 

 a nail-mark below the conical eminence (c.oii.)^ 



Fig. iki — Side view of an ovum in which the invaciination has y-one a little 

 further. 



Fig. i)b — Dorsal view of the same ovum. The conical eminence is con 

 verted into a flattened and broad elevation (cm.s.), the embry- 

 onic shield, and consequently the boundary groove (b.g.) is curved 

 anteriorly. 



Fig. ik — The same ovum froln tht- basal surface". The crescentic blasto- 

 pore (bp.) has increased in length of both its limbs. 



