CLEAVAGE IN THE EGG OF CEREBEATULUS. 15 



not the primary egg-axis coi-responds to the secondary axis induced 

 by centrifugal force does not concern us. Besides experimental 

 evidence we have a few observations sliowins; that cleavasce «roes 

 on normally irrespective of the variation in the distribution of 

 yolk granules (Lillte '01, zur Strassen '06). In all probability, 

 therefore, it is safe to conclude that the cleavage pattern is not 

 governed by granular localization. 



It is hardly necessary to state that cleavage pattern is intimate- 

 ly related with germinal localization. Yet these two are some- 

 times found dissociated, as we see in the egg of Cerebratulus, 

 in which, at a period when the morphogenic factors are already 

 established (Yatsu '04), the factors of cleavage pattern are not 

 yet fixed as we have seen in Exp. A. In the sea-urchin egg the 

 cleavage factors seem to establish themselves in one- cell stage, 

 when the morphogenic factors are still rather vague (Driesch 

 '96, Appendix I, pp. 104-112). In Denlalium Wilson ('04, pp. 

 42, 43, 66, 67) found that despite the removal of a portion of 

 the polar lobe material, the polar lobe of normal proportion is 

 formed. Ziegler ('08) and myself have made during subsequent 

 cleavages experiments on the egg of Bero'è with the results that 

 from which the vegital region has been removed, micromeres 

 are formed in normal size-relation in eggs. An interesting 

 observation was made by Lillte ('09, pp. 63, 64) on the egg of 

 Chœiopierus, that nucleated fragments freed of yolk granules 

 by centrifuging the egg, divide unequally into two cells of normal 

 proportion. Lastly in Cerebratulus, as described under Exp. E, the 

 proportion between the upper and lower cells of the 8-cell stage 

 is normal even in the egg, from which a portion of vegital region 



1 The results are still unpublished. 



