INTERNAL ANATOMY OF INSECTS. 163 
less than two years. The eggs in the ovaries of the last 
vary infinitely in size; those that have entered the oviduct 
have arrived at maturity, while the rest grow gradually 
smaller as they approach the capillary extremity of the 
tubes, where they become at length invisible to the highest 
magnifier?. In many insects the eggs seem nearly to have 
reached their full growth previously to the exclusion of the 
female from the pupa; and this exclusion and the im- 
pregnation and laying of the eggs rapidly succeed each 
other. One moth (Hypogymna dispar), which is remark- 
able for the number of eggs she contains, sometimes de- 
posits them, even before they are fecundated, in the pupa- 
case’. But in other cases the sexual union is not so im- 
mediate, and some time, longer or shorter, is requisite 
for the due expansion of the eggs; and the ovaries of the 
animal swell so much, as often to enlarge the abdomen 
to an extraordinary bulk: this is seen in a very common 
beetle (Chrysomela Polygon) that feeds upon the knot- 
grass; but in no insect is it so striking as in the female of 
the white ants, whose wonderful increase of size after im- 
pregnation I have related to you on a former occasion *. 
I shall conclude this subject with a few observations 
upon ovo-viviparous insects ; supposed neuters, and hybrids, 
which, though they do not fall in regularly under any 
of the foregoing heads, may very well have a place in this 
letter. 
1. It has already been observed that there are a few 
ovo-viviparous insects’, the young of which exist in the 
ovaries at first as eggs, but are hatched within the body 
of the mother, and come forth in the living form of a 
* Swamm. i. 203. b. ¢. xix. f. 3. > Reaum. il. 66. 
© Vor lab: Vor wll; p. O4—. 
M 2 
