196 THE LESSER HOUSE-FLY AND THE LATRINE FLY 



On the ventral side of the larva, extending from segments IV 

 to XI, there is a series of pairs of small spiniferous papillae as 

 shown in fig. 88, each of which is situated at the end of a trans- 

 verse row of spines. Posterior to this transverse row of spines 

 there is a shorter row of spines, divided into four groups. The 

 anterior or prothoracic, spiracular processes are six to eight- 

 lobed, the usual number of the lobes being seven. The posterior 

 spiracular processes are very similar to those of F. canicularis. 

 Vogler (1900), who has given a good description of this larva, 

 illustrates the anterior spiracular processes with eight lobes, and 

 his figure of one of the posterior spiracular processes is not 

 very clear. 



The feathery character of the processes of F. scalaris is 

 probably associated with the fact that the larvae usually live 

 in substances of a semi-liquid character, where such processes 

 will be more advantageous than those of F. canicularis for life 

 in such a medium. It may be of interest to note in this connec- 

 tion that the spiniferous and branched lateral appendages of the 

 larvae of the genus Fannia were considered by Walsh (1870) 

 and probably by other entomologists, to be " branchiae " or gills. 



Walsh {I.e.) stated: "The larvae 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 

 able, after the manner of a fish, to extract the air from the 

 fluids around them," and he comjjares them to the gills of the 

 Ephemerid larvae. 



Prior to pupation the larva leaves the moist situation for 

 one of a drier character, and the pupation is similar to that of 

 F. canicular'is. 



F. scalaris is more commonly found than F. canicularis as the 

 cause of intestinal myiasis, and it also breeds more commonly in 

 human excrement. These facts make its economic relation to man 

 one of some importance. 



