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 5 . 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 (Cht*y- 

 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. /. xix./. 3. 



c Reaum. ii. 66. A VOL. II. p. 36. 



