846 On Aquatic Carnivorous Coleoptera or Dytiscide. 
edge of the middle tibia: none of the legs 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 stigmata. 
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- 
bide, or in the Dytiscidze, 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 Carabide 
and the Dytiscide ; Lacordaire classified it among the Dytiscidee, while Schaum 
described it asa Heteromeroid form of Carabidee, 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 [ have decided to give Amphizoa a place, but a quite isolated one, 
amongst the Dytiscidee, for the following reasons :— 
The peculiarities of the Dytiscidze 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 Carabidze 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 
antennz of the Dytiscide are different as regards their sensitive structure from 
those of the Carabidz 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 Dytiscidee 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 Dytiscidee 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 
Carabidee and Dytiscide are perfectly in accordance with differences in their 
environment. 
* The special reason may be either, that the physical impulses acting on the antenne are not transmitted 
through water ; or that water in contiguity with the apparatus of sensation is incompatible with its 
functional activity. 
