sault. The gopher is singularly exempt from the dangers encountered by the species which normally dwell on the surface, and its needs are totally different from its purely terrestrial kindred. How is it, then, that the form remains unchanged? Clearly the selectionist has to assume either that advantageous variations do not occur, or that there is some controlling element limiting the process of variation which absolutely prevents the accumulation of these chance modifications to a profitable end. Variations do occur in the shape of individuals. They seem to be about as plastic as other vertebrates in this regard. Here we must throw out the idea that the failure to produce advantageous modifications is due to the lack of variety on which selection can work. We are therefore reduced to the question-begging of which many naturalists now avail themselves in considering this process, and are compelled to say that there is a certain rigidity in the organization of the animal which prevents the accumulation of beneficial variations. This explanation is substantially like that of the doctor in Molière's play, who explained that "opium put people to sleep because of its soporific virtue"; but this does not suffice in the present case. It is worth while to note in this connection that, although the habits of the gopher have varied little with their peculiar habit of life, they have invented, as before noted, the very sufficient and ingenious custom by which they discharge the surplus earth from their burrows at the least expenditure of force and time. This peculiar intellectual adaptation appears to me one of the most interesting features connected with the life of this interesting animal.
- The only peculiar modification of the gopher's shell which can be deemed the product of selection with reference to its peculiar habits is the share-like projection of the plastron or lower shell, which is directed forward, and possibly serves in a slight way to divide the earth at the bottom of the burrow over which it crawls. My friend Mr. S. W. Garman, who has kept one of these creatures in captivity, has observed that the animal, by tilting the body downward at the anterior end, can project this share under the edge of a stone or into the crevices between two boards, and exercise a considerable amount of disruptive power by this process. If these creatures made their burrows in stony ground, it might be possible to conceive the structure as advantageous, but as they work altogether in fine-grained soils, I can not conceive that this curious projection is of any functional value.