On Aquatic Carnworous Coleoptera or Dytiscide. 23 
Hydaticides and Cybistrini and Laccophilus that the tenuity of the antenne becomes 
extreme ; in some of the larger species of Cybister, such as C. owas, the antennz 
are so long and slender, and the joints are so very feebly connected together that it 
is difficult to find in collections a specimen with these organs unbroken. In some 
genera of the family the males have the antenne distinctly different from the 
female, the difference being usually that the middle joints are more or less dilated 
and assume peculiar shapes; this sexual difference is seen to its greatest extent in 
the genus Noterus; in some Hydrovatini (especially in Hydrovatus aristidis) the 
antenne of the male are remarkable for their torm; in the males of some species 
of Sternopriscus the form of the antennee is excessively bizarre, and two or three 
species of Agabus (Dytiscus serricornis No. 755, e.g.) are remarkable inasmuch as 
the apical joints of the antenn are dilated in the male. 
The most striking peculiarity of the antennz of the Dytiscide, is that they are 
quite free from setz, from sensitive pubescence or from punctuation, their 
integument being quite shining and polished. In Pelobius however the very large 
basal joint of the antenne is very distinctly punctate; and in Amphizoa the 
antenne are still more considerably punctate, the four or five basal joints showing 
an extensive though rather irregular and obsolete punctuation, and the following 
ones being each in succession more sparingly punctured, so that only the apical 
joints appear entirely glabrous and shining. 
This condition of the antennze is one of the most important of the distinctions 
between the Dytiscidee and Carabidze, the members of this latter family having the 
antennee setose, and the joints, except the three or four basal ones, covered with an 
excessively fine, short, and dense pubescence which, in conjunction with numerous 
minute pits on the surface of the joimts, makes them dull, and is considered to be 
an external apparatus of sensation. This glabrous condition of the antenne in 
the water-inhabiting Dytiscidz is therefore of interest as helping us to interpret 
the function of the antenne in insects—a very complicated and difficult subject. 
There are certain facts which render it probable that the simple condition of the 
antenne of the Dytiscidee is not to be attributed directly to their aquatic existence, 
but is rather correlative with their not being in contact with the atmosphere. 
The species of Hydrophilus (aquatic beetles of the family Hydrophilide) breathe 
in a very peculiar manner, by protruding from the surface of the water the three 
apical joints of their aatennse, and by their means carry down a supply of air to 
the under surface of the body ; now it is a remarkable fact that these three apical 
Joints thus exposed to atmospheric influences are covered with a very dense and 
fine sensitive pubescence, while all the rest of the antenna which remains in the 
water is completely glabrous and shining like the antennz in Dytiscide. There 
are, moreover, certain Carabidze in which the sensitive pubescence of the antennze 
is nearly absent, and it is interesting to note that there is reason to suppose that 
these are species which in the perfect state are nearly or completely withdrawn 
2) 2 
