INTERNAL ANATOMY OF INSECTS. 165 
viviparous, as I have before hinted®, at one period of the 
year, that is during the summer, but strictly oviparous 
at the close of the year. From the experiments of De 
Geer, however, upon Aphis Rose, it would appear that 
this faculty is not conferred upon the same individuals, 
but only upon those of different generations of the same 
species ; all the generations being ovo-viviparous except 
the ast, which is oviparous”: nor does it appear, as has 
been sometimes imagined, that it is common to the whole 
genus. De Geer observed a species in the fir, which 
makes curious galls resembling a fir cone (Aphis Abte- 
tis), which appeared never to be ovo-viviparous°. 
With regard to scorpions, it does not seem clear that 
they are always ovo-viviparous: M. Dufour twice found 
in the midst of the eggs nearly mature, a young scorpion 
which appeared to him at large in the cavity of the ab- 
domen; it was so large that it was difficult to compre- 
hend how it could possibly be excluded from the animal, 
without an extraordinary operation’. The pupiparous 
insects (Hippobosca, &c.) have been sufficiently noticed 
before °. 
2. I have already in several of my former letters stated 
to you what the modern doctrine of physiologists is with 
respect to certain individuals, usually forming the most 
numerous part of the community with insects living in 
society, that were formerly supposed to be newters, or as 
to their sex neither male nor female—that they are in 
almost every instance a kind of abortive females, fed with 
a different and less stimulating food than that appropri- 
ated to those whose ovaries are to be developed, and in 
a Vor Ts pel7a: » De Geer iii. 70—. 
© Ibid. 128. 4 N, Dict. d’ Hist. Nat. xxx. 426—. 
© Vor. IIL. p. 64—. 
