POST-EMBRYONIC DEVELOPMENT OF CULEX. 187 
_by it in his flight directly towards her. The larger eyes 
will also, no doubt, help him when he is at shorter 
distances. 
The compound eyes are already present in the larva, 
and in the pupa they rapidly increase in size till they 
almost envelope the head. The one point in their develop- 
ment of which I have convinced myself is that the growth 
consists in the addition of new elements at the edge, which 
arise by direct modification of the previously unmodified 
epidermis around the margin of the eye—epidermis whose 
last function was to secrete the pupal cuticle. The cells 
of this epidermis proliferate in groups, and the centre of 
each group becomes ‘‘invaginated,” the four cells round 
the margin of the invagination persisting as the ‘ nuclei 
of Semper’ immediately beneath the corneal cuticle which 
they appear to secrete. The invaginated portion gives rise 
to all the other parts of the eye which le outside the limit- 
ing membrane, with the probable exception of trachez and 
their ‘‘ peritoneal’ investment, and of the pigment cells. 
During pupal hfe vision must be very imperfect, for 
both the compound eyes and the ocelli he beneath the 
pupal cuticle and in the later stages are not even in con- 
tact with it. The ocelli ought probably to be regarded as 
the persisting visual organs of the larva, the compound 
eyes as the rudiments of organs to be first used when the 
imago emerges from the pupal exuvie. 
Of the reproductive organs, the ovaries (or testes) are 
present in the larva as a pair of fusiform bodies lying in 
the sixth segment (of the abdomen) at the sides of the 
intestine. Each is enveloped in a “peritoneal” layer of 
flattened cells. During pupal life this investment grows 
backwards to form the paired oviducts of the female, or 
the anterior part of the vasa deferentia of the male. The 
remaining organs of the female are a median oviduct (often 
