CLEAVAGE AND DEVELOPMENTAL PATTERN 



595 



only as regards diminution but also as regards products of later cleavages 

 (Boveri, 1910a, b). Boveri's conclusion that polarity in the Ascaris egg 

 is a gradient was drawn from these cleavage patterns of dispermic eggs. 

 Although the earlier normal cleavages of Ascaris are highly determinate, 

 it appears from the dispermic eggs that a physiological cytoplasmic pat- 

 tern persists independently of the alteration of cleavage pattern; but 

 whether it is quantitative or regionally specific remains uncertain. Since 



Fig. 185, A-C. — Diagrammatic outlines of cleavage of dispermic Ascaris eggs. A, three 

 AB cells, one Pi cell; B, two AB, two P^; C, one AB, three Pi (modified from Boveri, 19106). 



dispermic eggs give rise, not to normal individuals, but only to cell masses, 

 it is evident that something is wrong with developmental pattern. Ac- 

 cording to Boveri, eggs with one ventral cell (Pi) develop more nearly 

 normally than the other types. 



Entrance of more than one spermatozoon occurs normally in eggs of 

 urodele amphibians, but the supernumerary spermatozoa and their cen- 

 ters take no part in development and disappear. Experimental poly- 

 spermy in anuran eggs, resulting from high sperm concentration, alters 

 cleavage because the number of centers equals the number of sperma- 

 tozoa, but only one sperm nucleus unites with the egg nucleus. Di- and 



