6 AIlï. 11. s. H ATTA. 



hindered by tlie mass lying within, and the inward pressure is 

 thus converted into one directed against the part lying in front 

 of and dorsal to it, the part thus pressed showing itself as the 

 conical eminence {Fig. 5a, c. em.). When finally, the resistance 

 to the inward movement is overcome, the flattened area moves 

 further inwards towards the segmentation cavity as a continuation 

 of the process of invagination and thus the blastoporic depression 

 is finally established. When this is done, the conical eminence 

 is at liberty to subside, becoming low^er and flattened out. 



It is further evident that the boundary groove is a product 

 of the same process, though passive in origin : along the junction- 

 line between the translucent and opaque halves, the thin wall of 

 the translucent hemisphere is connected with the upper edge of the 

 opaque half; and when the conical eminence is protruded, it is only 

 the opaque j)art which takes part in this protruding. Thus, as 

 the part below the junction-line protrudes while the part above 

 it is kept distended by its liquid contents, and as the junction-line 

 remains in its original position, there is necessarily j^roduced a 

 constriction along this line between the two j^arts ; and this con- 

 striction is nothing but the boundary groove. Accordingly, the 

 demarkation of the groove against the opaque part, which is at 

 first faint, becomes sharp and distinct with growing elevation of 

 the eminence. I have observed that at that time the groove appears 

 to be brought nearer to the base {Mgs. 4a and 5a, bg.) than 

 before, — a phenomenon denoting the progressing invagination of the 

 opaque hemisphere. The ventral view of the ovum remains as 

 yet unaltered. 



The appearance and subsequent disaj^pearance of the 

 conical eminence were doubtless observed by Max Schultze^\ 



1) loc. cit., p. ?• 



