230 DISEASES OF INSECTS. 



place with respect to the whole in less than half an hour. 

 When entirely disengaged, they place themselves close 

 to the sides of the caterpillar : even before this they be- 

 gin spinning, and draw unequal threads in different di- 

 rections, of which they form a cottony bed, which serves 

 as the base of the separate cocoon of each individual, 

 which they next construtt of a beautiful silk thread of a 

 lovely yellow, which, if it could be unwound and in suffi- 

 cient quantity, would yield a silk unrivalled in lustre and 

 fineness a . 



De Geer has recorded a very singular fact which de- 

 serves your notice. An Ichneumon, appropriated to one 

 of the Tortrices, had deposited its eggs in two of their 

 caterpillars ; each produced a considerable number ; but 

 those that emerged from one were all females, and those 

 from the other, males b . He observed a similar fact take 

 place with Misocampus Puparum c . One might conjecture 

 from this circumstance, that as in the queen-bee d , so in 

 these Ichneumons, the eggs producing the two sexes 

 were arranged separately in the ovaries. Reaumur has 

 related, that in one instance three or four males were 

 produced to one female ; and in another four or five fe- 

 males to one male e . 



But though the great majority of insects are subject to 

 this Scolechiasis f in their larva state, yet sometimes they 

 are not attacked by the Ichneumon till they have become 

 pupa. Of this kind is one just mentioned (M. Puparum), 

 which commits its eggs to the chrysalis of the butterfly 

 of the nettle, Vanessa Urticce : the moment this cater - 



* Reaum. ii. 419. b De Geer i. 583. 



c Ibid. ii. 884. rt See above, p. 164. 



c Reaum. vi. 312. f VOL. I. p. 99. 



