44 THE AMPHIOXUS. 



rather unequal. There is a great difference to be 

 noticed between the segmentation spheres of the 

 upper half and those of the lower half. We can 

 continuously observe the main axis drawn from the 

 upper to the lower pole, from the unfertilized stage 

 up to the formation of the bias tula. 



"When we look more closely at the segmentation 

 of the Amphioxus in reference to the characteristic 

 succession of the planes of segmentation, we recog- 

 nise that it shows in the main the same type as 

 does that of the lower vertebrates, which have a 

 holoblastic development (Petromyzon, Sturgeon, and 

 Amphibia). That is to say, we find an extensive 

 agreement which was not to be recognised from the 

 accounts hitherto published. 



The segmentation begins, as Kowalevsky says, 

 about an hour after the liberation of the eggs. The 

 formation of the first furrow and the division of 

 the egg follow then very quickly, that is, in about 

 five minutes. It is just the same with the suc- 

 ceeding divisions. After a somewhat long interval 

 the division of the segmentation spheres begins, 

 its completion being followed by an interval as 

 before, 



