342 N. YATSU : OBSERVATIONS AND EX PERIMENTS 



formed half-cleavage as in an isolated blastomere of the 2-ccll stage 

 (Fig. III. 25 and 26). 



IV. Summary and Conclusions. 



The egg cleavage of Callianira Inalata differs from that of Berci 

 in the following points : 



1. The third cleavage plane is sometimes horizontal ; in other 

 cases there is a tendency to be so. 



2. The fourth micromeres arc budded off from the end-cells. 

 The following are the results obtained from the experiments per- 

 formed upon the egg of Berci- ovata. 



1. If a portion of cytoplasm is removed from the egg before 

 the commencement of the first cleavage, the nucleated fragments cleave 

 like a whole egg. 



2. If the egg be split into two during the first cleavage, each 

 nucleated fragment divides as half-cleavage, as in isolated blasto- 

 meres of the 2-cell stage. 



3. If the egg be cut along any plane into nucleated and non- 

 nucleated fragments during the first cleavage, the former divides like 

 a whole egg, forming micromeres in thenor mal way. 



4. End-cells are more variable in size than middle-cells in 

 operated eggs, especially when these are small. 



5. Size of micromeres depends principally upon that of the frag- 

 ments producing them and not upon the quantity of ectoplasm contained 

 in these. 



6. Size of the micromeres from the end-cell is not proportional to 

 that of its macromere in operated eggs. 



7. Micromeres seem to have a tendency to keep their proper 

 size as various operations show. 



8- Egg fragments, from which a large portion of the micromere 

 pole has been removed before the fourth cleavage, are capable of 

 producing micromeres. 



