ART. 10. — N. YATSU : 



I. Experiment A (C laeteus). 



This series of experiments consists in cutting off a portion 

 of cytoplasm from the egg along oblique planes^ at different 

 periods extending from the formation of the first polocyte to the 

 beginning of the first cleavage {cf. AVilson '03, p. 430). Twenty 

 seven eggs were thus experimented on and the early cleavage 

 stages were studied. Without giving the record of each case, the 

 results may be summarized as follows : (a) the cleavage of twelve 

 eggs operated on between, the formation of the first and second 

 polocyte was regular (Figs. 1-4). In two eggs out of twelve the 

 cleavage went on somewhat irregularly with regard to the arrange- 

 ment of the blastomeres. This was undoubtedly due to the tempera- 

 ture, which was unusually high on the day the two eggs were 

 operated on ; (b) of fifteen eggs cut between the formation of the 

 second polocyte and the first cleavage, nine divided regularly, 

 while the rest cleaved abnormally regarding both size-relation 

 and rhythm (Figs. 5-7). 



From this experiment it will be seen that in the egg of C. 

 lacteus the mode of cleavage is disturbed by the removal of a 

 portion of cytopasm in a short period preceding the first cleavage. 

 The statement I made in a previous paper, that enucleated 

 fragments taken before the first division cleaved always regularly 

 ('04, pp. 134-135, 136), is, therefore, not altogether correct and 

 should be modified as just stated. 



1 Since horizontal cut is liable to cause normal cleavage, ohliqiie sections were puvpo?ely 

 performed in this series. 



