RECENT DISCOVERIES IN INSECT EMBRYOGENY. 
121 
voured by the cannibal it has sheltered or procreated. The case, 
therefore, is one of true larval propagation, or, as it it is usually 
termed, u agamic reproduction.” The organic matter which 
produces the brood increases as the larvae develop, and the 
membrane in which it is enclosed serves ultimately as an invest- 
ment, a “ cocoon” for each young embryo before it is disengaged 
and thrown into the general cavity of the body. 
This reproduction of larval broods continued from August till 
May, when the last set of larvae acquired sexually distinct 
characters, after passing through the usual metamorphosis, and 
becoming mature insects. We had occasion, in a recent num- 
ber, to describe the larvation of the aphis, and it seems here 
worthy of remark, that the time of year at which viviparous lar- 
vation occurs in the aphis, is exactly the contrary of that during 
which the propagation of the recently discovered Cecidomyia 
larvae goes on. This fact appears to militate against the hypo- 
thesis that the functional activity of the reproductive organ 
depends on the influence of external temperature, but, on the 
contrary, favours the assumption that it depends rather on the 
supply of food, the aphis obtaining its nourishment from the 
summer juices of plants, whilst the winter larva of the Cecido- 
myia feeds on aliment prepared and deposited under the young 
bark after the sap changes of the warm season. 
But this phase of reproduction proved to be transitory ; for, 
as summer advanced, the larva became a pupa, in which sexu- 
ally distinct forms were already visible, and, in the course of four 
days, perfect male and female insects appeared. The insect 
proved to be dipterous. The male, having an expansion of wing 
equal to that of the female, but a comparatively much slighter 
body, possesses considerable power of flight. The female is, as 
usual, a larger-bodied insect, and produces five remarkably large 
eggs, which fill the whole abdomen, and contain a yolk-mass, 
from which the fatty tissue of the new larva is derived. The 
successive larval broods are, in turn, nourished at the expense 
of this fatty substance. 
The cycle of genetic phenomena is the same, therefore, as in 
other creatures in whom “ alternate generations” are observed. 
The insect egg has a smooth shell, and is furnished with a fun- 
nel-shaped open-mouthed micropyle. The first larva developed 
from this egg contains fatty tissue from which the subsequent 
broods spring, according to Wagner, who (at the time of 
his published memoir), affirmed that no special reproductive 
organ existed. This view of the origiu of the larval progeny 
coincides, therefore, with Wagner’s account of the histologic 
relations of the germ elements. He describes the embryonal 
reader is referred to an interesting chapter in Dr. Lawson’s felicitous trans- 
lation of Quatrefages’ work on metamorphosis (page 74 et seq.). 
L 2 
