Object and Function of the Egg-stalk. 123 



to stream first into the egg-stalk and afterwards back 

 into the egg-body. But there is a point of still greater 

 importance — the egg-stalks of Cynipidae are not similar 

 in origin and formation to those of the other hymeno- 

 ptera. If we examine a stalked egg of Tryphon, the 

 stalk is ver}^ differently formed ; it appears as a solid 

 appendage to the egg-envelope, and is to be regarded 

 as a cuticular formation. It is intended to be bored 

 into the skin of caterpillars. The stalk of Cynipidae 

 eggs has a totally different intention. It is not a simple 

 appendage, but contains a cavity in direct connexion 

 with the yolk sac ; and its extremity has a club-like 

 dilatation. Therefore part of the yolk can enter the 

 egg-stalk without difficulty, and, as has already been 

 stated, this actually occurs each time an egg is laid. 

 This peculiar form of egg seen in Cynipidae can easily 

 be recognized within the ovarian follicles in an earlier 

 stage of development. In Plate III, Fig. 9, part of 

 the egg-tube of Neuroterits fumipennis is represented 

 exhibiting the origin of the egg-stalk. On the younger 

 egg-germ nothing is yet to be seen of the stalk, and the 

 yolk mass has assumed a cylindrical form ; in the 

 more developed egg-cell the flask-shaped form of the 

 yolk shows plainly the egg-stalk in course of formation. 

 Later the younger egg-cells, as seen in the last egg, 

 develop egg-stalks and come to lie finally against 

 the wall of the egg-tube, overlapping each other like 

 tiles. To appreciate exactly the intention of the egg- 

 stalk, it is necessary to observe a still later stage of 

 embryonic development, at which it sometimes occurs 

 that the egg-body expands and enlarges to a remarkable 



