54 [July, 
which, though abnormal, enables them to be of service to the 
creature. In the entire absence of connecting links, it requires a 
considerable amount of faith to believe that these changes can 
have been brought about by natural selection, especially as it 
requires a liberal use of the imagination to conceive the steps by 
which they could have been effected. 
The four posterior legs differ entirely from the anterior ; they 
are short, compressed laterally, so as to resemble considerably the 
fins of a fish ; and while in the Dyiiscidce swimming is facilitated 
by the attachment of peculiar hairs to legs but slightly modified 
from the ordinary type, in the Gyrinidce swimming hairs are also 
present, but the entire leg is remarkably modified, and developed 
into an organ exclusively suited for the purposes for which it is 
destined. Moreover, in the Dytiscidw only the hind pair of legs 
are specially modified, while in the Gyrinidce this is the case with 
both the middle and hind pairs. 
Though the peculiar distinctness of the Gyrinidce as a group, and 
the absence of anything like connecting links between them and other 
beetles, would seem to be opposed to the idea of their being connected 
by descent with other Coleoptera, yet the fact that within the bounds of 
the group the species are very closely allied, yet variable, and that it is 
not easy to fix with certainty the limits of some of the species, appears 
to be favourable to the theory that all the Gyrinidcd may have descended 
originally from some one species. The difficulty above adverted 
to of distinguishing the species of Gyrinus from one another is not 
diminished by the fact that they are generally found in little colonies, and 
that these colonies often consist of two or three species ; sometimes 
the most allied species being found together, and at other times the 
most dissimilar. 
We have in Britain two genera of this family ; they are very easily 
distinguished by the following characters : — 
1. Body entirely destitute of pubescence, extremity of abdomen broad, 
and rounded at its apex — Gyrinus. 
2. Body covered with a thick, short pubescence, extremity of abdomen 
conical — Oeectochilus. 
1. — nTRiNDS, Geoffroy. 
Our species of Gyrinus may be arranged in three groups — 
* Under surface entirely testaceous — G. minutus and urinator. 
