286 GNATS OR MOSQUITOES — CHAPTER XII 



prominent specific characters vary a good deal, so that it is 

 usually possible to find aberrant specimens of any one species 

 which more or less resemble those near it ; and an extension of 

 the kind of argument used to deprecate the so-called " multipli- 

 cation of species " might easily be made to reduce them to 

 absurdity by showing that in this way the whole genus, or family, 

 if it comes to that, is but a single species ; but in spite of this, 

 where we find Mosquitoes presenting given characters, which run 

 fairly true through a long series of individuals ; it is certainly 

 more convenient to regard them as distinct than to confuse our 

 ideas by the enumeration of the endless catalogue of possible 

 variations that must be appended to specific definitions in any 

 attempt to cut down the nominal number of species. 



There is hardly any character relied upon in systematic work 

 that does not vary considerably in Mosquitoes, and the value 

 even of anatomical characters cannot be pushed too far, as the 

 relative positions of the longitudinal junctions of the longitudinal 

 veins, and the distance apart of the transverse veins, which are 

 often recorded at great length in many descriptions, often vary 

 so much that they would better be left unrecorded. The general 

 relative position of the transverse veins with respect to each 

 other indeed does not, so far as can be made out, vary, so that 

 we shall not find the posterior, e.g., sometimes internal, and at 

 others external, to the middle transverse; but their distance 

 apart, as may be seen in the figures of two specimens of Grassi's 

 pseitdopictus, $ , plate viii, figs, lib, lie, varies so greatly in the 

 same species that it is quite useless to record such points, unless 

 found constant in a long series of specimens ; but the position of 

 the cross-veins with x'espect to eacli otlier, though not their pro- 

 portional length or distance apart, is of considerable value in 

 distinguishing species, and is given, for ready reference, in tabular 

 form on following pages. 



In this table, and elsewhere, for the sake of brevity the 

 mathematical sign for parallel, " ||," is used to signify " opposite," 

 or " in one line with " ; and where 3 (the middle transverse 

 vein) is placed external to the other two venules, the arrangement 

 is stated as "alternate"; where, on the other hand, they are 

 placed like the steps of a stairway, 2 (the supernumerary) 

 being placed outermost, and 4 (the posterior) innermost, it is 

 given as " seriatim." 



Coquillett, I understand, doubts if even the form of the tarsal 

 claws is constant, but the larvae of allied species are so often 

 found associated in one puddle that it may be suspected that the 



