THE ANATOMY OF THE LARVA 41 



quently that this was a mistake due to the occurrence of 

 several species in the same pool, and that a ratio of this 

 sort remains fairly constant throughout the growth of the 

 larvae. It is easy, for example, to distinguish between the 

 larvae of G. fatigans (Wied), and those of the species I 

 identify as C. impellens (Walker), which constantly are 

 found associated here in the cold weather, the breathing 

 tube of the former being of medium length, while that of 

 the latter is very short ; and I have met with larvae in 

 which the syphon is so short that they may easily be 

 confused with those of Anopheles, the more so as they 

 not unnaturally assume much the same position in the 

 water ; but I was unable to delay my departure in order to 

 ascertain the species to which they belonged, but I believe 

 they were those of a Stegomijia. 



In Anopheles, on the other hand, apart from size, the 

 larvEe of different species are most difticult to distinguish. 

 Their coloration is singularly alike, and as yet I could not 

 undertake to distinguish those of any individual species, 

 though they differ considerably in the matter of the size 

 of the anal tubercles. 



Quite recently Grassi {G.S.Z., p. 81) has shown that 

 the bristles with which these larvae are provided, in various 

 situations, differ sufficiently in the various species to be 

 made use of to afford definite indications of the species to 

 which a larva belongs. Tliese bristles are often of very 

 complex structure, and this is especially the case with those 

 on the dorsum of the thorax and head. Confining his 

 attention to those of the latter region, he finds that the 

 characters of two special bristles, viz., the sub-median pair, 

 in the middle of the fore border of the head, and those 

 placed at its external angles, suffice to easily distinguish 

 the four European species of Anopheles larva3 known to 

 him, and on comparing his figures with the corresponding 

 bristles of the larvae of An. Bossii, I find that in that species 

 too these bristles again differ from any of those. It will be 

 observed that the difference between the bristles of An. 

 liossii, as compared with those of An. superpictits, is very 

 marked, and is alone quite sufficient to set at rest any 



