THE EGG. 31 



After the egg lias been in the plant a few hours, it 

 swells up to more than double the size it was when 

 laid, while at the same time the receptacle in which it- 

 was deposited has widened, and, it may be, blackened. 

 Thus, instead of being beneath the epidermis (or twig 

 as the case may be), it now projects out of it. The 

 cause of this swelling is obscure. It is certain that 

 when the egg was laid, a drop ("Westwood* calls it a 

 " drop of frothy matter") of liquid was laid in the 

 incision along with it, but I do not think that this 

 has anything to do with the swelling of the egg. Its 

 purpose seems rather to be to widen and keep open 

 the incision made for the reception of the ovum, so 

 that its sides may not crush it ; and probably, too, it in 

 sonic way causes moisture to flow to the incision from 

 the surrounding portions. According to Newport,! 

 on the second day after the egg was laid the incision 

 expanded so much that " a free space remained around 

 the egg equal to its own width on each side." West- 

 wood { further remarks that the eggs imbibe "nutriment 

 in some unknown manner through their membranous 

 skins from the vegetable juices which surround them." 



The swelling takes place before the form of the 

 larva can be seen in the egg, which can usually be 

 done on the third day. Whether the development of 

 the larva is ever retarded for a much longer period is 

 a point about which I have no definite information. 



I think, however, it is very probable that with 

 Enipliijtus serotinus (which appears in the perfect state 

 at the end of September and October) the eggs remain 

 unaltered during the winter. We must either assume 

 that, or that the larvse appear when the leaves are 

 about gone, that they hibernate in a very young state 

 while the winter lasts, and then come out with the 

 young leaves in the spring. 



* Intr., ii, 95. f Prize Essay, p. 23. J L. c., p. 96. 



