[11] A Text-book of Zoology, Parker & Haswell, 1897.
[12] The Cambridge Natural History, vol. V, 1895, vol. VI, 1899.
[13] A Manual for the Study of Insects, J. H. and A. B. Comstock, 1897.
[14] It has been shown by experiment that the winged individuals, which are able to leave the old food-plant and scatter over new plants, do not appear until the food-supply begins to run short. At the insectary of Cornell University ninety-four successive generations of wingless individuals were bred, by taking care to provide a constantly abundant supply of food. This experiment was continued for more than four years.
[15] The animals included by some zoologists in the single class Pisces, are held by other zoologists to constitute three distinct classes, thus making a subdivision of the branch into ten classes.
[16] The author wishes to call the attention of teacher and student to the plan (referred to in the Preface, page v) adopted in writing the directions for the dissections. The sequence of the references to the various organs depends on the actual course of the dissection, and not upon the association of organs in systems. And the directions are so much condensed that they are hardly more than a means of orienting the student, leaving him to work out independently, or by the aid of more detailed accounts (sometimes specifically referred to), the details of the dissection.
[17] By many zoologists the lizards and snakes are held to form two distinct orders, Lacertilia and Ophidia.
[18] One of the most unfortunate and conspicuous examples of this slaughter is the partial extermination of the song-birds of Japan in the interests of European milliners. To meet their demands the country people used birdlime throughout the woods with disastrous effectiveness, as shown in the present exceeding scarcity of birds and the abundance of insect pests.
[19] Oysters are hermaphroditic, each individual producing both sperm- and egg-cells.
[20] Jordan and Kellogg's "Animal Life," 1900, p. 274.