44 ^^^ A ceo UNT 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 larva 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 strobi). 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. sisymbrii inhabits a gall on Berberis vulgaris in May and June, 

 and a gall on Nasturtium sylvestre from June to November. 



Again, there are larvge that live as guests* in the galls of other 

 species. It is a general rule to find several larvae in company with 

 one another. {Diplosis with Hylesinus and Apion in the stems of 

 Sarothriuni scopariiun. ) 



The larvae 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 Diplosis 



■ceoniatis) ; 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 larvae, 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 forniing gall-like masses in the flower-heads. 



On leaving the egg-membrane the larvae (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 larv^ 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 

 larvae fourteen joints instead of the normal number, thirteen. 



The head and mouth parts do not seem to be properly under- 



Often called *' inqtiilines" from the Latin inquilinus, a guest, or sojourner. 



