338 RICHARD ASSHETON. 



his figures of the segmenting ova of the dog, or guinea-pig, or 

 deer, and only in a less degree in the rabbit. Van Beneden 

 (4) for the rabbit described a cap of smaller segments, which 

 ultimately surround a group of larger cells. I was in a former 

 paper unable to offer evidence in support of this. Heape (15) 

 found nothing of the kind in the mole. 



When, however, we take into consideration the recent 

 account given by Duval (13) for the bat, and Hubrecht (16) 

 forTupaia, of a growth of slightly smaller cells round a core of 

 slightly larger cells, which is made much more obvious by 

 reason of a difference in the affinity to stains of the two groups 

 of segments, and an account of a similar process in the sheep, 

 which I hope to give in an accompanying paper, together with 

 the original description of the rabbit as given by Van Beneden 

 (although subsequent observers have been unable to confirm 

 his statements), it is clear that there is much evidence in 

 favour of this original discovery of Van Beneden ; and in the 

 present case I have to consider whether the specimens I have 

 described above of the segmentation in the pig may indicate 

 an identical wrapping round one group of segments by another 

 or not. It seems extremely probable that there is such a pro- 

 cess. Its significance, however, I have discussed in my paper 

 on the Development of the Sheep (la), in the last number 

 of this Journal, whose development I believe shows that it is 

 really the hypoblast which grows round the epiblast, and not 

 vice versa, as Van Beneden supposed. 



Formation of Cavity of Blastodermic Vesicle to 

 Rupture of Zona radiata — Stage C. 



The surrounding membrane consists still of the zona 

 radiata, which is becoming slightly stretched (fig. 15). In this 

 figure the vacuolation seems to be more pronounced at one 

 part than elsewhere. 



I am inclined to think that this more intense vacuolation 

 eventually leads to the origin of the cavity of the blastodermic 



