304 STATES OF INSECTS. (Jmago.) 
elytra of the females of many of the larger water-beetles 
(Dytiscus) are deeply furrowed, while those of the males 
are quite smooth and level*. ‘The thorax of the female 
in several species of Colymbetes of the same tribe, as 
C. Hybneri and transversalis, on each side has several 
tortuous impressed lines or scratches, like net-work, 
which are not to be discovered in the male. Hyphydrus 
gibbus, which differs solely from Hl. ovalis in being 
thickly covered with minute impressed puncta, is, from 
the observation of the Rev. R. Sheppard, the other sex 
of this last, with which he has taken it coupled; and 
it is by no means improbable that Hydroporus picipes 
(Dytiscus punctatus Marsh.) and H. lineatus,—between 
which, as Gyllenhal has justly observed, the same dif- 
ference only exists,—are in like manner sexual varieties. 
With respect to pubescence, I have not much to say. 
Another aquatic beetle, Aczlius sulcatus, has not only its 
elytra sulcated, but the furrows of these, and a trans- 
verse one of the thorax, are thickly set with hair; while 
the male is smooth, and quite naked. Particular care 
seems to have been taken by the Creator, that when all 
the above inhabitants of the water are paired, the male 
should be able to fix himself so firmly, by means of his 
remarkable anterior tarsi, (which I shall afterwards de- 
scribe,) and these asperities, &c. in the upper surface of 
his mate, as not to be displaced by the fluctuations of 
that element, the reluctance of the coy female, or any 
other slighter cause. 
* There is a section of this genus, or a subgenus (Leionoti K.MS.), 
to which D. cireumecinctus belongs, in which the female has smootk 
elytra like the male. I received one long ago from the Rev. Mr. 
Dalton of Copgrove, Yorkshire. 
