44 AN ACCOUNT OF BRITISH FLIES. 
The egg of the Cecidomyia is rounded at each end and slightly 
elongated, yellowish to white in colour, The period of hatching is 
extremely variable, some ova taking weeks-to develop ; some can, by 
artificial warmth, be made to hatch in a few hours. 
The larva.—The food of the Jarva is mostly vegetable ; some live. 
on decayed wood, others under the bark of trees, and some few are 
said to be saprophytic, but most are true vegetable feeders, living on 
the soft parts of leaves and stems of plants. 
A few have also been recorded from fungi, and some from pine- 
cones (C. strovi). They each have definite plants to live upon, and 
are seldom found on widely-different genera. ‘There are, of course, 
exceptions to this rule, as shown by Winnertz, who points out that 
C. sisymbrit inhabits a gall on Berberis vulgaris in May and June, 
and a gall on WVasturtium sylvestre from June to November. 
Again, there are larve that live as guests* in the galls of other 
species. It is a general rule to find several larvae in company with 
one another. (Dz¢plosis with Aylesinus and Aion in the stems of 
Sarothrium scoparium.) 
The larvze mostly live inside the vegetable tissue and produce the 
so-called galls, destroying, stunting and deforming the tissues of the 
plants. There are also some that live outside the plants (as Dzf/osis 
ceomatis) ; and others, as the Hessian-fly and Wheat Midge, that live 
in the axils of leaves and amongst the florets of wheat. 
As to the various deformations produced by these larva, it is not 
possible to enter here into all the numerous varieties produced. 
‘They vary from rounded protuberances attached by stalks to the 
stems of plants to rugosities and swellings on leaf and stem, arresting 
the growth and often destroying the reproductive faculties of the 
plant by forming gall-like masses in the flower-heads. 
On leaving the egg-membrane the larve (Fig. 9) are colourless and 
transparent, the alimentary canal being seen through the body-wall, 
often assuming a green appearance, derived from the vegetable food 
it has been consuming. The whole larva, as it advances in age, 
_ becomes opaque, and assumes a reddish appearance, or sometimes 
a yellowish colour. ‘ 
One striking peculiarity of these larve is the number of joints. 
Between the head and first thoracic there is placed a supernumerary 
joint ; to which segment this belongs we cannot say; it might 
belong to either the head or the thorax. Thus we have in these 
larvee fourteen joints instead of the normal number, thirteen. 
The head and mouth parts do not seem to be properly under- 
* Often called ‘* czguzlines,” from the Latin zzguclinus, a guest, or sojourner. 
