214 On Aquatic Carnivorous Coleoptera or DytiscidcB. 



from the air on account of their completely subterranean existence ; we may 

 therefore conclude that it is under the influence of much exposure to the atmosphere 

 that the sensitive pubescenca on the antennas of beetles has been developed. The 

 more elongate exserted setae present in the Carabidre but absent in the Dytiscidaj 

 have probably a totally different function from the fine sensitive pubescence ; it is 

 quite possible that they are tactile organs similar to the whiskers of the cat, and 

 that they are absent in the Dytiscidpe because the resistance of the water when the 

 insect is active would move the setre, and, if they are as I have supposed sensitive 

 to pressure, render them a nuisance to their possessor. The study of these 

 structures falls however to the Carabophilist, but I must remark in connexion 

 with the question of the relations between the Carabidse and Dytiscidse, that in the 

 former family there exists considerable differences in the clothing of the antennie ; 

 tlms in the rare and anomalous Trachypachys there is a complex and symmetrical 

 system of antennal setaj, but sensitive pubescence seems to be entirely absent ; 

 while in other cases, as in Anthia, there is a beautiful development of the 

 sensitive pubescence and a nearly complete absence of setse. In the Scaritidae and 

 Broscidiie the four basal joints of the antennae are glabrous (except that in some 

 Broscidaj porosity begins at the apex of the fourth joint) but on the other joints the 

 rule is that the porosity is confined to the edges of the more or less compressed 

 joints, the flattened sides being glabrous. Exceptions occur in %vhich the porosity 

 covers the whole of these joints, and there are other exceptions —these much more 

 remarkable — in which the porosity is almost entirely absent. It is especially 

 noteworthy that the forms presenting this latter peculiarity are those which from 

 their form and appearance, are probably most completely subterranean in their 

 habits, such as Monocentrum, Teratidium, Neocarenum, Passalidius, and 

 Metaglymma. In Passalidius there are neither punctures nor hairs, but there are 

 grooves on the edges of the joints. In Neocarenum there exists scarcely any 

 pubescence but a few coarse punctures. In Scarites excavatus there are large 

 punctures mixed with the fine porosity on the edges of the joints. Thus we see 

 that in the subterranean Carabidae, where the antennre are less subject to atmos- 

 pheric influences than the other members of the family, the antennce have their 

 sensitive structures less largely developed than usual, and that in the most completely 

 subterranean forms of the family the antennas approximate to those of the aquatic 

 Dytiscidae, without however being so completely simple as in the water beetles.'^'" 



* I am greatly indebted to Mr. H. W. Bates for furnishing to me the information above recorded 

 about the sensitive structures of the antennae in the Scaiitini and Broscini. Mr. Bates has examined 

 many species in the following genera with the results thus tabulated — Carcnum, Pasimachus 

 Emydopterus, Euryscaphus, Carenidium, O.vylobus, Scaraphites, Crepidopterus ; in the above the 

 compressed joints 4—11 are glabrous only along the middle of the flattened sides ; while in Monocentnim 

 Teratidium, Neocarenum, Passalidius, Metaglymma, Brullea, the antenna; have a diminished band of 

 jiorosity on the edges or are entirely smooth; in Scarites they are much as in Carenum but more, 

 variable ; in Gnathoxys there are rather distant pores, and in Percosoma there is dense porosity. 



