8 AFxT. 11. — S. IIATTA. 



the form of ii widely gaping funnel, the dorsal part of which is 

 wanting. The funnel formed would be entire if the opaque field 

 were pressed down in the direction of the long axis of the ovum 

 (cf. Fig. 17) ; but instead of that it is pushed dorsad and forwards, 

 that is, in an oblique direction making an angle of some 60° with 

 the axis {Fig. 17, hp.), so that a half-funnel is brought about. 

 This sinking down of the opaque half is nothing but a part of 

 an extended invagination of tlie lower hemisphere of the ovum. 



The arc of the blastoporic lip attains its maximum extent 

 in the stage when it describes about a semicircle {Fig. 7c). At 

 tliis time the blastoporic funnel is represented by a large hollow 

 excavation ; the hind part of the opaque hemisphere which is 

 sickle-shaped in outline still shows a convex surface. From this 

 stage on, both the limbs of the arc are brought nearer to each other ; 

 /. e.f the angle contained in it grows less {Fig. Sc, bj).). And at 

 the median deepest point of the funnel the blastoporic passage is 

 converted into a circular pore. The convergence of the arc-limbs, 

 however, goes on only until they assume the shape given in 

 Fig. Sc, and stops long before the rest of the opaque hemisphere 

 has all been changed into a concave surface ; and this shape of tlie 

 blastopore is kept up until the entire withdrawal of the opaque part 

 within the ovum. When this is nearly accomplished the blastopore 

 shows a feature similar to that in earlier stages and is reduced 

 into a small oval depression still wanting the . ventral lip- {Fig. 

 10a). Tlie depression is then gradually converted into a circular 

 pore {Fig. lib, bp.) which constitutes the definitive blastopore. 



This transformation of the oval depression into the circular 

 pore is, as is very well seen in Fig. 11, brought about by 

 the upheaval of the hitherto'' non-existant ventral margin 

 of the blastopore. The ridge thus formed is nothing 



