Variation. 



Lastly, there is the difficult question of variation. To any one 

 who has read Mr. Theobald's monograph carefully it will be 

 apparent that he takes little or no account of the numerous varia- 

 tions which occur among the different species of mosquitoes, and 

 that he considers the slightest differences, often microscopic, 

 as of specific value. In the limited space at our disposal it is 

 impossible to describe even the structural variations which are met 

 with in members of the same species of mosquito, but by taking an 

 example we may note the slender grounds upon which many of 

 Mr. Theobald's species are based. For this purpose we may 

 consider the four mosquitoes, funestus, listoni, culicifacies 

 and rhodesiensis. In the first volume of Mr. Theobald's 

 monograph these four species are distinguished from one another 

 chiefly on account of differences in the relative positions of the 

 cross veins of the wings a character upon which, as being struc- 

 tural, the author laid much stress. We were able, however, to 

 show that even in a series of individuals of any species from 

 the same batch of eggs the relative positions of the cross veins 

 varied greatly, and in the third volume of his monograph Mr. 

 Theobald admits that the character is of no value as a means of 

 differentiating closely allied species, and relies entirely upon colour 

 differences. As regards funestus he says : "It comes very 

 near listoni, but can be at once told by the palpal banding 

 being different, the three white bands being unevenly disposed, 

 the two apical ones being nearer together than in listoni The latter 

 species has also a very prominent white-scaled third longitudinal 

 vein ; in funestus it may be entirely dark or may have a white 

 patch, but is never so markedly pale as in the Indian species." Thus 

 the two points upon which Mr. Theobald relies for specific distinc- 

 tion are differences in the palp banding and differences in the mark- 

 ings of the third longitudinal vein. Unfortunately, however, he 

 is not consistent, for in the preface to this volume he says : "These 

 (palp) bands are only colour effects, and specific distinctions cannot 

 be based on such ; moreover, specimens may frequently be met with 

 showing variations in this respect." He also recognises that great 

 variations occur in the markings of the third longitudinal and other 

 veins of the wings, and describes two varieties of funestus, in one 

 of which the third longitudinal vein is dark, as in rhodesiensis 



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