Mammals are stuffed with cotton or tow; the latter is used in species from a gray squirrel up. Large mammals stuffed with cotton do not dry readily, and often spoil. Being much thicker-skinned than birds, mammals require more care in drying and ordinarily require a much longer period. Soft hay may be substituted for tow; never use feathers or hair. Roll a longish wad of cotton about the size of body and insert with forceps, taking care to form the head nearly as in life. Split the back end of the cotton and stuff each hind leg with the two branches thus formed. Roll a piece of cotton around end of forceps and stuff fore legs. Place a stout straight piece of wire in the tail, wrapping it slightly to give the tail the plump appearance of life. (If the cotton cannot be reeled on to the wire evenly, leave it off entirely.) Make the wire long enough to extend half way up belly. Sew up slit in belly. Lay mammal on belly and pin out on a board by legs, with the fore legs close beside head, and hind legs parallel behind, soles downward. Be sure the label is tied securely on right hind leg. For directions for preparing and mounting skeletons of birds, mammals, and other vertebrates, see the books of Davie and Hornaday already referred to. _Fishes, batrachians, reptiles, and other animals._--The most convenient and usual way of preserving the other vertebrates (not birds or mammals) is to put the whole body into 85 per cent alcohol or 4 per cent formalin. Batrachians should be kept in alcohol not exceeding 60 per cent strength. Several incisions should always be made in the body, at least one of which should penetrate the abdominal cavity. Anatomical preparations are similarly preserved. By keeping the specimens in glass jars they may be examined without removal. Fishes should not be kept in formalin more than a few months, as they absorb water, swell, and grow fragile. Of the invertebrates all, except the insects, are preserved in alcohol or formalin. The shells of molluscs can be preserved dry, of course, in drawers or boxes divided into small compartments. FOOTNOTE: [21] The following directions for making skins of mammals were written for this book by Mr. W. K. Fisher of Stanford University, an experienced collector. INDEX --Illustrations are indicated by an asterisk _Acanthia lectularia_, *188. Acarina, 230. _Acmara spectorum_, *248. Actinozoa, 97, 102. Adaptation, 407. Adder, spreading, 321. _Ægialitis vocifera_, 349. Agalenidæ, 235. _Agkistrodon piscivorous_, 323. _Aix sponsa_, 347. Albatross, 346. _Alca impennis_, 345. _Alce americana_, *385, 396. Alligator, 326. _Alligator mississippensis_, 326. Alternation of generations, 96. _Amblophtes rupestris_, 282. _Amblystoma_, 297, 298. _Amblystoma maculatum_, 299. _Ameiurus_, 282. _Amœba_, *32; structure and life of, 31. _Amphioxus_, 278. Anaconda, 324.