INTERNAL ANATOMY OF INSECTS. 169 
greater proportion of insects, some exclude the whole 
number in a very short period, others require two or 
three days or a week, as the cockroach a ; and others, as 
the queen-bee, not 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 capil- 
lary extremity of the tubes, where they become at length 
invisible to the highest magnifier b . 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 impregnation and laying of 
the eggs rapidly succeed each other. One moth (Hy- 
pogymna dispar), which is remarkable for the number 
of eggs she contains, sometimes deposits them, even be- 
fore they are fecundated, in the pupa-case c . But in 
other cases the sexual union is not so immediate, and 
some time, longer or shorter, is requisite for the due ex- 
pansion of the eggs ; and the ovaries of the animal swell 
so much, as often to enlarge the abdomen to an extraor- 
dinary bulk : this is seen in a very common beetle (Chry- 
somela Polygoni) 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 impregnation 
I have related to you on a former occasion d . 
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 fore- 
going heads, may very well have a place in this letter. 
* De Geer iii. 533. b Swamm. i. 203. b. t. xix./ 3. 
c Reaum. ii. 66. d Vol. II. p. 36. 
