Eyes and auditory conchæ feebly developed, feet for scraping, tail lax; live always under the ground, and eat roots and grains—Spalax, Rat, Common and Field-mouse, Beaver; mostly only three molars.
Fam. 2. Polypary Thricozoa—Klettermäuse.
Eyes, ears, and tail large, the latter being stiff and hairy, claws pointed; live mostly upon trees, eating nut-kernels and fruit; usually four molars—Squirrels.
Fam. 3. Acalephan Thricozoa—Laufmäuse.
Eyes and ears large, tail hairy, hind feet longest, claws obtuse, lamellar or plicated teeth; live upon the surface of the earth and eat grass—Hares and Guinea-pigs; mostly more than four molar teeth.
Order 2. Ader-, Geschlechts, Schalthier-Haarthiere—Kaumäuse.
3568. Teeth and toes deviating completely from those of every other order; nor in a less degree the method of propagation.
In some instances all the teeth are wanting, in some they exceed the ordinary number, and are quite uniform; sometimes the lateral teeth only are similar, but in this case there are no canines and incisors; or else there are canines with more than six incisors, or also with rodent teeth.
In like manner the toes are irregular; the one kind being disproportionately large and the other absurdly small; some are for the most part wholly connate; in many cases there are hands posteriorly. The claws also are in some instances obtuse, in others sharp for climbing, or else asymmetrically large and unciform. Hands adapted for swimming or flight also occur.
Finally, the sexual parts are quite aberrant, being mostly very large and singularly formed; the mammæ frequently lodged in a pouch, or at least furnished with marsupial bones. The young are born as naked and immoveable embryos, and suckled for a very long time.