On Aquatic Carnivorous Coleoptera or Dytiscida. 213 



Hydaticides and Cybistrini and Laccophilus that the tenuity of the antennae becomes 

 extreme ; in some of the larger species of Cybister, such as C. owas, the antenna 

 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 antennas 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 

 antennas of the male are remarkable for their form; in the males of some species 

 of Sternopriscus the form of the antennas 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 antennae are dilated in the male. 



The most striking peculiarity of the antennae of the Dytiscida?, is that they are 

 quite free from setae, from sensitive pubescence or from pvmctuation, their 

 integument being quite shining and polished. In Pelobius however the very large 

 basal joint of the antennae is very distinctly punctate ; and in Amphizoa the 

 antennae 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 antennae is one of the most important of the distinctions 

 between the Dytiscidas and Carabidae, the members of this latter family having the 

 antennae 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 joints, makes them dull, and is considered to be 

 an external apparatus of sensation. This glabrous condition of the antennae in 

 the water-inhabiting Dytiscidae is therefore of interest as helping us to interpret 

 the function of the antennas in insects — a very complicated and difficult subject. 



There are certain facts which render it probable that the simple condition of the 

 antennee of the Dytiscidre 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 Hydrophilidfe) breathe 

 in a very peculiar manner, by protruding from the surface of the water the three 

 apical joints of their aatennte, 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 pubsscence, while all the rest of the antenna which remains in the 

 water is completely glabrous and shining like the antennae in Dytiscidae. There 

 are, moreover, certain Carabidae in which the sensitive pubescence of the antennae 

 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 



