oj some species of Clirysomela, §'c. 173 



to separate tlie individual from the original type, and 

 develop it into a distinct species ; in a third, from 

 adverse causes, the species may be on the eve of total 

 extinction. 



I have omitted all mention of sexual selection, which 

 doubtless plays an important part in the gradual modifi- 

 cation of animals, more especially in the development of 

 sexual differences ; but I have said enough to show that, 

 in the minds of all who hold the above views, the concep- 

 tion of a species and of its limits must stand on a broader 

 basis than the one entertained by the older naturalists. 



Individuals will occasionally be met with (as, for example, 

 in Ch. sanguinolenta and allied forms), so closely on the 

 border-line between variety and species, and presenting 

 such slight differences of structure, that they may be 

 placed, with almost equal justice, under either head; with 

 these exceptions, the absence of structural characters will 

 reduce an individual, differing only in minor particulars, 

 to the subordinate rank of a variety (local or otherwise) 

 of a previously-known specific group. 



In the vertebrata3 and higher animals good characters 

 are often found both in the skeleton and in the soft internal 

 organs ; in the invertebratte and lower forms of life, the 

 softer parts are generally unavailable for use, and cha- 

 ractei'S must be sought in the outer surface of the body. 



In insects the part of the body where these characters 

 reside vary in almost every family. In the Chrysomelidce 

 they are found in the tarsi, the palpi, the margination and 

 shape of the sides of the thorax, in the arrangement of the 

 punctuation of the elytra, in the apical segment of the 

 abdomen, and more rarely in the antennee ; lastly, the 

 telum or $ organ* (in many groups quite useless as a 



* The telum or $ organ may be separated into the following parts: — 

 (1) the body, a hollow corneous tube, variable in length, and more or less 

 curved longitudinally, the convexity of the curve beiug upwards ; its lower 

 surface is prolonged anteriorly into (2) the apex, the variations in form of 

 which afford valuable diagnostic characters ; its upper or convex surface is 

 shorter than the lower and terminates anteriorly in (3) the valve, a corneous 

 or semi-corneous plate, continuous at its base with the surface of the body, 

 but free at the sides and apex ; when sufficiently rigid to retain its shape 

 after death, it is frequently of use in separating closely-allied species ; 

 lastly (4), the duct, a slender, apparently tubular body, lying in the cavity 

 of the telum ; this last is often short and entirely hidden from view, but fre- 

 quently extends beyond the anterior margin of the valve or even beyond 

 the apex of the telum itself ; it is sometimes slender and filiform, at other 

 times more robust and rigid ; its apex is very variable in form. 



In medium sized or large Coleo])tera the telum can always be extracted 

 without the slightest injury to the specimen ; the mode I adopt is as 



