DIPTERA— MUSCIDxE. 551 



Family MUSCID^E Leach. 

 MUSCA Linne. 



Under this head I have temporarily placed five species of dipterous 

 larvge which appear to belong to this family. 



Nearly all of them, however, and especially Musca ascarides, so closely 

 resemble the larvae of bot-flies that I could scarcely persuade myself that 

 they did not belong to the (J^stridaj. The appendages of the skin, how- 

 ever, are much more delicate than is usual in (Estrida^, and are uniforndy 

 distributed over the surface or are altogether absent. The empty skins, 

 too, have every appearance of belonging to the same insects as the com- 

 plete bodies, and, although these are not cast skins (in which case they 

 would be proved natural inhabitants of the water), for they still contain 

 the harder parts of the internal organs in many cases, but rather remains 

 of partially decomposed larvae, it would seem improbable that so large a 

 number of oestrid larvte could be found, when the only way in which they 

 could have reached their present condition would be through the droppings of 

 animals affected by the bots standing in tiie water. Of course the refei'- 

 ence I have given them is only provisional. 



Musca ascarides. 



PI. 5, Figs. 74, 75, 79, 82-87, 98, 101. 

 Musca ascarides Scudd., Bull. U. S. Geol. Geogr. Siirv. Terr., Ill, 750-707 (ls77). 



First there is a species to which a considerable numljer of specimens 

 belong, which may take the name here given. Some of the specimens are 

 complete; others consist of emptied skins only. When contracted the 

 body is thick, especially on the anterior half, and about twiee as long as 

 broad, closely resembling the larva of a bot-fly. Both extremitii's are 

 nniiided, the anterior very broadly, while the posterior half tapers very reg- 

 ularly. In one specimen, which is not so much shrunken, the body is 

 fusiform, and about three and a half times longer than broad, the head 

 and hinder extremity tapering in a nearh' equal degree. In the emptied 

 skins, as in the others, it may be seen that the normal form is a blunt, 

 squarely rounded head, behind which the body is nearly equal, and then 

 tapers toward the tail. At the anterior extremity may be nearly always 

 seen a portion of the mandibles, consisting of a pair of ver}' slender rods or 



