846 On Aquatic Carnivorous Coleoptera or DytiscidcB. 



edo-e of the middle tibia: none of the lesfs are in the least incrassate or modified for 

 swimming: and the tibia of each is terminated by two short, subequal spurs. 



The sexual distinctions are unknown to me, as also are the position and condition 

 of the stiofmata. 



The above characters are drawn from a specimen of Amphizoa insolens, Lee. 



Amphizoa is peculiar to California, it is a completely isolated creature and yet at 

 the same time a so-called synthetic type. 



It has been much discussed whether the genus should be classified in the Cara- 

 bidse, or in the Dytiscidse, or should form a distinct family : and some of the ablest 

 of modern Coleopterists have treated the question. Leconte, the original describer 

 of Amphizoa, considered it the type of a family distinct both from the Carabidae 

 and the Dytiscidae ; Lacordaire classified it among the Dytiscidae, while Schaum 

 described it as a Heteromeroid form of Carabidie, and another entomologist actually 

 described the insect as a member of the Heteromera. I am with Horn unable to 

 detect the least approach to the Heteromera, and think Schaum's opinion quite 

 incorrect. For each of the opposing views of Leconte and Lacordaire much may 

 be said, and I have decided to give Amphizoa a place, but a quite isolated one, 

 amongst the Dytiscidae, for the following reasons : — 



The peculiarities of the Dytiscidae have been produced in accordance with two 

 main facts of their existence, first that they live in the midst of water, and second 

 that they locomote through and in that medium : while the Carabidse live on the 

 surface of the earth, or do so approximately ; the structural peculiarities of the 

 two families are correlative with this difference of the conditions of existence The 

 antennae of the Dytiscidae are different as regards their sensitive structure from 

 those of the Carabidae because the medium through which the origin of the 

 sensations is conveyed is different ■* so the locomotive organs in the two families 

 act under profoundly different conditions, the legs of a Carabus walking on dry 

 ground have to overcome the influence of gravity and both lift and support and 

 move forward the being at each step ; the Dytiscidae are of nearly the same specific 

 gravity as the fluid in which they live, but are a little lighter than it, and their 

 legs have to act so as to slightly drive down their bearer at they same time as 

 they move it forwards ; the legs of a Carabus find the medium which directs their 

 action only beneath their body, and only a small portion of the limb can come in 

 contact with this medium, while the Dytiscidae have the whole body and leg sur- 

 rounded by the medium ; hence the leg as a lever acts in a different direction, so 

 that it may be quite correctly said the differences in structure of the legs of the 

 Carabidae and Dytiscidae are perfectly in accordance with difl'erences in their 

 environment. 



* The special reason may be either, that the physical impulses acting on the antennse are not transmitted 

 through water ; or that water in contiguity with the apparatus of sensation is incompatible with its 

 functional activity. 



