DEVELOPMENT OF SPELERPES BILINEATUS 



175 



filled with an albumenous fluid, surrounds the egg, e, to which is 

 closely applied a very thin delicate vitelline membrane,^ seen in 

 the living egg only when the embryo begins to appear. 



Occasionally two eggs are enclosed in a common membrane. 

 One case was noted in which the outer gelatinous layer enclosed 

 three eggs, two of which w^ere closely packed into a common 

 perivitelline space, while the third had its own. 



Fig. P 



The liquid in the perivitelline space is under considerable pres- 

 sure, for when the membranes are punctured they collapse sud- 

 denly, while the fluid squirts out with considerable force. If the 

 egg be shelled from its membranes into a dish of water, it con- 

 tinues to develop for a time. The egg is very soft and flattens 

 somewhat from its own weight. The first cleavage furrow in 

 such an egg has been seen to flatten out into a broad trough, in- 

 stead of the narrow furrow described below. Eggs, when removed 

 from their membranes, if kept in sufficiently cold water may reach 



^Van Bambeke ('80) calls this membrane the chorion. 

 * Descriptions of figures are given in the text. 



