54 CLEAVAGE II 



A. Nucleate and enucleate egg-fragments are taken of the 

 same size ; both are fertilized, and develop. The number of 

 cells in equal areas of the same germ-layer, at the same stage, 

 is then counted. 



For example : 



Nucleate fragment Enucleate fragment 



Ectoderm of anal area . 167 317 



Ectoderm of ciliated ring 86 163 



B. The number of cells in larvae from monaster eggs is 

 compared with that in normal larvae. 



For example : 



Monaster (4 n). Normal (2 n). 



Blastula .... 23 43 



Pluteus (animal ectoderm) 37 71 



It is clear that at the same stage in larvae derived from the 

 same original quantity of cytoplasm, the number of the cells in 

 equal areas of the same tissue is inversely proportional to the 

 number of chromosomes in the nuclei. 



C. In partial Arrhenokaryosis and partial Thelykaryosis the 

 larva is obviously composed of two regions (separated usually 

 by the median plane) in which the size of the nuclei is differ- 

 ent. The number of small (n chromosomes) nuclei is to the 

 number of large (2 n) as 2 : 1. 



We turn to the relation between the number of chromo- 

 somes and the size of the nuclei as measured not by their 

 diameters but by their surface-areas. The initial amount of 

 cytoplasm in each case is constant as before. 



A. Merogonic and nucleate egg-fragments. 



Nucleate fragment Enucleate fragment 



In gastrula stage . 42 21 



In pluteus stage . 46 25 



B. Partial Arrhenokaryosis. 2n($+a*)' n 

 The two sides of the pluteus are compared 27 14 



C. Partial Thelykaryosis. 2 n (? + <>*). n (?). 

 The two sides of the pluteus are compared 30 14 



D. Diplokaryosis ; the monaster egg is com- 



pared with the normal. Monaster (4?t). Normal (2 n). 



66 33 



