THE CELLULAR BASIS 167 



of chromosomes in cleavage is abnormal the 

 larva shows abnormal characters (Boveri) ; 

 sex determination is associated with the distri- 

 bution of a particular chromosome to one-half 

 of the spermatozoa, and the f ertihzation of the 

 ^SS ^Y one type or the other of spermatozoa 

 (Wilson) ; the linkage of certain characters 

 with sex finds a ready explanation by assimi- 

 ing that the differential causes of these char- 

 acters are associated with the sex chromosome 

 (Morgan). 



2. Cytoplasmic Correspondences. — On the 

 other hand the most direct and the earliest 

 recognized correlations between the oosperm 

 and the developed animal are foixnd in the 

 polarity and symmetry of the fertihzed egg 

 and of the animal to which it gives rise. 



(a) Polarity. — In all eggs there is a polar 

 differentiation, one pole, at which the matura- 

 tion divisions take place, being known as the 

 animal pole, and the opposite one being known 

 as the vegetative pole. The substance of the 

 egg in the vicinity of the animal pole usually 

 gives rise to the ectoderm, or outer cell layer 

 of the embryo ; the portion of the egg sur- 



