On Aquatic Carnivorous Coleoptera or Dijti^cidw. 971 



the Dytisci frairiiientati have hut little connection with the D3-tisci complicati (only 

 the variable swimming leg and bare antennae), that the distinctions between the 

 Carabidae and Uytiscidse are not very important, and that on the other hand 

 the Dytisci complicati are distinguished by a character absolutely peculiar to them 

 among the whole enormous mass of Coleoptera, the question arises would it 

 not be a more natural classification to follow the structure of the coxal cavity, 

 treating it as of superior importance to the hind coxa and swimming leg ; and thus 

 massing together the Dytiscidie and Carabidfe into one whole comprising three series 

 determined by the number of jiieces entering into the structure of the coxal cavities. 

 I think it is probable that this would be an improvement, and content myself with 

 pointing it out to naturalists who may be inclined to discuss the very difficult 

 question of the classification of the families of Coleoptera. There is no harm in 

 mentioning that in the Mammalia the water-frequenting members are not classed 

 together because of the similarity in their forms and in their apparatus for locomotion, 

 but are distributed in different families on account of other peculiarities. 



If this view were adopted, and the modifications in the structure of the middle 

 coxal cavities wei'e considered as of predominant importance over the structure of 

 the hind coxse, we would, before long, have to discuss as to which of the three 

 forms of structure of the middle coxal cavities is the higher and which the lower. 

 The facts as genei'alized are very peculiar ; thus we find that the greater part of 

 the Carabidte have the coxal cavities formed by only two pieces ; that the smaller 

 first or fragmentary series of the CarabidiB, together with the first or smaller and 

 fragmentary series of the Dytiscidse, and the whole (?) of the Cicindelidse have 

 these cavities formed by three pieces ; while the greater part of the mass of the 

 Dytiscidee, including the higher forms of the family, have four pieces entering into 

 the formation of these parts. Now, as the Cicindelidge are, on the whole, the 

 highest of the families of predaceous Coleoptera, as they have fewer pieces to form 

 the cavities than have the Dytisci complicati, it would appear that cavities formed 

 by a small number of pieces were characteristic of a higher grade of organization 

 than those with more jiieces in their composition ; but against this must be set the 

 tact, that the higher Dj^tiscidas have more pieces in these cavities than have the 

 lower Dytiscidaj. It would thus appear that however important may be the 

 structure of these cavities as a means of classification, it is not at present in 

 relation with general perfection of the organization. And the explanation of the 

 anomaly may probably be found in the fact that the mode of formation of these 

 parts was determined at a very early period of the development, and when the 

 present gradations as to higher and lower did not exist. That the primitive con- 

 dition of these parts of the thorax and legs may possibly have been extremely 

 different to what we find it at present, may be inferred by an examination of 

 Biatta in the Orthoptera, where we find the coxse to be enormous in size, while 

 the thoracic pieces are correspondingly reduced ; now, although this is a very 



TRANS. nOT. DUD. SOC, H.S, VOL. II. 6 1 



