A. H. Lees 257 



membrane, but subsequent more careful examination showed these 

 to be the two edges of the hollow process of the middle membrane. 



The larva is entirely shut off from the hollow processes by the 

 inner membrane and the mouth parts in every specimen examined 

 were found curled up anteriorly and ventrally. On hatching the outer 

 and middle membranes are left with their processes imbedded in the 

 twig. 



Morphology and function of egg membranes. In most insect eggs 

 two membranes can be observed, the inner, or oolemma, and the outer, 

 or chorion. The latter is often divided into exo- and endochorion 

 connected by chitinous trabeculae, the ends of which in surface view 

 give rise to the sculpturings of the outer egg shell. It is clear that in 

 the case of Psylla mail the inner membrane is the oolemma and the outer 

 is the chorion. It is difficult to see what the middle membrane corre- 

 sponds to. 



The relation of the egg coverings is peculiar and suggestive. If 

 the object were simply to secure an anchoring mechanism the outer 

 process would seem sufficient. It is possible, however, that there may 

 be some physiological connection between the egg and the apple twig. 

 The facts already quoted of the close relation between the time of 

 hatching and the time of bud bursting in different varieties of apples 

 would seem to suggest this. Until more direct evidence is obtained, 

 however, it would be premature to press this hypothesis. 



Ann. Biol, n 17 



