immature sexuality in Insects. 199 
The facts I related at the commencement of this paper, 
referred exclusively to the Ametabola. I have not ob- 
served that the larve of the Metabola ever become truly 
sexually mature, but I think I shall be able to show that 
it is highly probable the phenomenon of viviparous ge- 
neration in the gall-gnats, arises from the early maturation 
of the ovaries. 
It has been already noticed that the sex of the Meta- 
bola may be discovered by an examination of the sexual 
organs of the embryo some time before birth. I have 
only observed the development of these organs in the 
blow-fly, and in this insect they are the only larval organs 
that are continuously developed, and which persist in the 
adult fly. 
There are only three structures in the larva, which do 
not undergo disintegration during the development of the 
pupa. These are the imaginal discs, the nervous system, 
and the sexual organs. The imaginal discs do not persist 
in the perfect fly; they unite and form a pupa-skin, en- 
tirely homologous to the pupa-skin of a moth or butterfly ; 
the dried larval skin becoming converted into a kind of 
cocoon. The nervous system undergoes rapid redeve- 
lopment, new structures being formed to subserve new 
functions; the sexual organs, alone, undergo ordinary 
development. * 
I think we see the effect of the accelerated development 
of ovaries, in the viviparous agamic generation of Ceci- 
domyian larve. Dr. Leuckart’sf observations leave no 
doubt, in my mind, that the germ stocks of the Cecido- 
myian larva are actually modified ovaries, and that the 
development of the new larva, within the body of the 
mother, is the result of the non-development of the 
accessory sexual organs, the oviduct, vagina, &c. The 
agamic nature of the process is no objection to this 
theory, as we know that parthogenesis is by no means 
uncommon amongst perfect insects, even when they are 
ready to produce young in the ordinary way. 
I cannot refrain from quoting Leuckart’s own expres- 
sion on this subject :—‘‘ The asexual propagation of the 
* For further details, see my work on the ‘Anatomy of the Fly.’ 
+ Ann. Nat. History, 1866. 
p 2 
