III. Changes Preliminary to Cleavage. 



The history of the changes which traTis])ire between the stage 

 of maturity and that of cleavage — "the jjrehjde to the cleavage- 

 drama/' as Auerbach terms it — forms one of the most inter- 

 esting chapters in the biology of the egg. 



So far as yet known, these changes in the egg of Clepsine 

 are unsurpassed in variety by those of any other nf^^j.. 



Some of them take place on the surface and can be easily 

 followed on the living egg, by the aid of a simple lens ; while 

 others are accomplished in the interior, and, owing to the 

 opacity of the yolk, can only be traced by means of sections. 

 In order to connect these two series of phenomena, in such a 

 manner that the events of one series may be placed in chrono- 

 logical relation with those of the other, it is necessary, first of 

 all, to know the sequence of the surface changes. This known, 

 it becomes possible to describe intelligibly the eggs that are to 

 be hardened for sections. 



With a view to making sections I have adopted the following 

 course : — The time is divided into three periods, the first ex- 

 tending from the time of deposit to the appearance of the first 

 polar globule ; the second, from the first polar globule to the 

 lirst polar ring; and the third, from the first polar ring to the 

 cleavage. Using the time of dej)osit, of the first polar globule, 

 and of the first polar ring as three j)oii)ts of departure, eggs 



