SHARP: HYDRADEPHAGA OF LANCASHIRE AND CHESHIRE. Igt 
none of these genera or species are in any way modified as regards 
structure. However much they may delight in wetness, it is only 
actual life in the waters that is potent to alter shape. Nevertheless, 
it cannot be doubted but that a long series of semi-aquatic and onl 
partially modified ancestors must have existed before such perfected 
forms as Dytiscus or Hydrcphilus began to be. 
We have already stated that this group of Hydradephaga—highly 
specialized as it is—is in fact merely Geodephaga expressly modified 
to an aquatic life. Let us then consider the links of union which 
show that such is the case. In the first place they are all equally 
predacious and carnivorous. Now in relation to the affinities of 
insects, the character of their food may appear an unimportant point; 
it is however, in reality of the first magnitude, because the whole 
structure of an insect and all its economy is arranged primarily in 
relation to the character of its food, not the food to the structure. 
That is an important point to notice; for instance, it is not because 
Cicindela (tiger beetle) possesses those powerful and ruthless jaws, 
those agile legs, and ready wings, not because it has been endowed 
with all these, that it therefore seeks its food by the capture of other 
insects only less swift and less powerful than itself; but that the 
need of such and no other sustenance has induced the means most 
fitted to secure that end. ‘The character of food then goes deeper 
than structure, because it occasions it, and we find a bond of union 
between Geodephaga and Hydradephaga in that both live on other 
living organisms, captured by their superior means of offence. But 
further, proceeding to a consideration of morphological similarities, 
we find that in both these groups there are invariably five tarsal joints 
for each leg in both sexes. No beetle has more than five—just as no 
vertebrate has more than five digits—although whether there be any 
significance in the parallelism we will not now consider—but many 
beetles have fewer tarsal joints than five. Some of the other groups 
are very irregular in this matter of tarsal joints, some having four, some 
only three, some different numbers on different pairs of legs, some 
differing according to sex, but superior to all these aberrations we find 
all the Geodephaga and all the Hydradephaga have always five joints 
in all the legs in both sexes, although it must be admitted in some few 
€ases one joint is rudimentary. Furthermore, in both these groups 
we find similar mouth organs or trophi and similar antenne. Now 
among all the organs on which various classifications of the Coleoptera 
have been based, the antennze have always been given a prominent 
Position, and the mouth organs according to their greater or less 
development differentiate with the utmost precision the minor as 
well as the major groups. 
June 1892, 
