DIPTERA. -— MUSCID&. 563 
The insects of this family are of small and moderate size, and of 
very variable habits; the larva feeding upon various substances both 
animal and vegetable, and both in a dead and living state. These 
larve are in general apod, soft, vermiform, annulated grubs, of a cylin- 
drical-conic form, attenuated in front, and thickened and obtuse 
behind, with a head of variable form, furnished with two retractile 
hooks; the terminal segment of the body, in many, and also that im- 
mediately succeeding the head, furnished with two spiracles, in some 
species inserted upon horn-like appendages. The pupa, which is very 
immature in its form, with a swollen head (Réaumur, Mém. tom. iv. 
pl.21.; Westwood, in Mag. Nat. Hist. March, 1835), is enclosed 
within the contracted and indurated skin of the larva, which sometimes ; 
assumes the form of an oval horny exarticulate mass, but in other 
species retains more of its former appearance. De Geer (Mém. tom. vi. 
tab. 1—6.) and Réanmur (Mem. tom. iv.) have figured the transform- 
ations of various species of this family ; but it is difficult, if not impos- 
sible, to determine with precision the insects represented by them. 
Some idea of the extent of this family may be obtained, from Meigen 
having described nearly 1700 European species ; and about the same 
number (belonging, however, only to a portion of this family, and 
forming upwards of 350 genera), having been described by Robineau 
Desvoidy, in his Essai sur les Myodaires, a quarto volume of 812 
pages, most of which species are extra-European. In England 700 or 
800 species have already been recorded, which is probably not more 
than two thirds or one half of the actual number of indigenous species. 
Hence, as well as from the great diversity in the structure and 
habits of the numerous tribes of which the family is composed, it is 
not surprising that the study of the Muscide is attended with great 
difficulty, and can scarcely indeed be said at present to be more than 
commenced. The works of Latreille, Meigen, Fallen, Wiedemann, 
Desvoidy, and Macquart, have done much to reduce this immense 
mass to something like order; but the difficulties attending the 
subject are far from being smoothed, nor can the arrangement of 
these tribes be perfected until we are better acquainted with the 
habits and transformations of many of the groups. 
It is to Latreille, Fallen, Desvoidy, and Macquart, that we are 
indebted for the attempts which have been made to establish sub- 
families and other sectional groups, facilitating the study of the 
species; but these groups differ in extent in the works of these 
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