138 



THE AMERICAN ENTOMOLOGIST. 



tion, wallow in moist decaying matter, whether 

 animal or vegetable ; and as in such situations 

 they would be sometimes stifled for want of 

 air, if they breathed through the spiracles or 

 breathing-holes with which all air-breathing- 

 insects are supplied, nature has replaced the 

 spiracles by lateral "branchiae" or gills, by 

 means of which they are enabled, after the 

 fashion of a fish, to extract the air from the fluids 

 that surround them. On referring to our Fig- 

 ure 93, b, the reader will see at ouce the structure 

 of these curious gills, whicli. however, are by 

 uo means peculiar to this genus of Insects, but 

 occur in a great number of larvas that inhabit 

 the water, for example in those of the Mayflies 

 (Ejihemera family). These larv;e dift'er further 

 from those of the true Flower-flies in the tail 

 end being much less conspicuously docked, and 

 in the body being considerably flattened, in- 

 stead of plumply louuded in the shape of an 

 elongate cone. It was probably in reference to 

 this peculiar flattening of the body of the larva, 

 that Bouche gave to the genus the distinctive 

 name of "Flat-fly" (Homalomi/ia), from two 

 Greek words which bear that meaning. 



In the perfect state — as sometimes happens 

 with closely allied genera— the Flat-flies do not 

 dift'er so materially in their structure and gen- 

 eral appearance from tlie true Flower-flies as 

 do the larva^ belonging respectively to these 

 two genera. Still, as the larval habits of these 

 two genera dift'er so widely, and as the Flower- 

 flies, in the original and more extensive signi- 

 fication of the term, form a very extensive 

 group — authors having described no less than 

 0.3 species of them as found in North America — 

 we must consider the separation of tliis very 

 large and unwieldy genus into two smaller 

 genera as a judicious step. The minute details 

 wherein the Flat-flies dift'er from the Flower- 

 flies in the perfect fly state, as they would only 

 fatigue the general reader, will be found in the 

 loot-note.* 



We have ourselves bred what Baron Osten 

 Sacken, to whom we have forwarded specimens, 

 thinks is in all probability a true Flat-fly, from 

 larva' very similar to those figured above, but 

 scarcely more than half as large {IIoDKtlomyia 

 prunifora). These larvie we met with in great 

 abundance in a mass of tame plums so much ; 



decayed as to become almost semi-fluid. The 

 fly produced from them is only about one-fifth 

 of an inch long; whereas from the largest spe- 

 cimens sent us by Dr. Wilson we might expect 

 to raise a fly at least one-third of an inch long. 

 If, therefore, there was no other reason than 

 this, we might be pretty sure that the two spe- 

 cies are distinct. But, as the scientific reader 

 will perceive from the descriptions given in the 

 foot-note, there are other reasons for believing 

 them to belong to sepai ite '■pecies ot 1 lat flies * 

 •iio \\ _; „ I 11 \,p 1 1 



til 

 Jumts 



'Tbroiigh the kiniliii'ss of Bavoii 0.steu Sackeu, 



i leavn 



Such sexual aistiuctious seem to br nut uuusual iu this gi-oup 

 of flies ; for Baron Ostea Saclcen infoniis us that ' ' the sex^ 

 in Anthomyia generally differ Tery considerably in size and 



ther Ijristly than 



diate in its characters between Wilsoni and prumiora. In 

 length it is said to be from 0.23 to 0.29 inch. The dorsal 

 branchioe seem to agi-ee generally with those of jirunioora. 



