pithecus). The gibbons, inhabiting southeastern Asia, possess arms of such length that they are able to touch their hands to the ground as they stand erect. They are thus adapted for a life in the trees, where they spend most of their time feeding on fruit, leaves, and insects. In the same district the orang occurs, walking when on the ground on its knuckles and the sides of its feet. It prefers the life in the trees, however, in

which it builds nests serving for rest and concealment. The gorilla (Fig. 140), the largest of apes, attaining a height of over five feet and a weight of two hundred pounds, is a native of Africa, where it lives in families and subsists on fruits. The same region is the home of the chimpanzee, which in its various characteristics approaches most nearly to man.

Man (Homo sapiens) is distinguished

by the inability to oppose the big toe as he does his thumba feature associated with his erect position-and by the relatively enormous size of the brain. Even in an average fouryear-old child or an Australian bushman the brain is twice as large as in the gorilla. With this relatively great development of the nervous system is correlated superior mental faculties, which together with social habits and powers of speech exalt man to a position far above the highest ape.

As usually understood, the family of man (Hominidæ) contains but a single species, cosmopolitan and highly variable. This species is "now split up into many subspecies or races, the native man of this continent, or 'American Indian,' being var. americanus. Other races now

naturalized in America are: the Caucasian race, var. europaus; the Mongolian race, var. asiaticus; and the negro race, afer. The first of these is an immigrant from Europe, the second from Asia, and the third was brought hither from Africa by representatives of var. europæus to be used as slaves."

CHAPTER XIX

THE LIFE CYCLE

231. Birth, growth and development, and death.-Certain phenomena are familiar to us as occurring inevitably in the life of every animal. Each individual is born in an immature or young condition; it grows (that is, it increases in size), and develops (that is, changes more or less in structure), and dies. These phenomena occur in the succession of birth, growth and development, and death. But before any animal appears to us as an independent individual— that is, outside the body of the mother and outside of an egg (i. e., before birth or hatching, as we are accustomed to call such appearance)-it has already undergone a longer or shorter period of life. It has been a new living organism hours or days or months, perhaps, before its appearance to us. This period of life has been passed inside an egg, or as an egg or in the egg stage, as it is variously termed. The life of an animal as a distinct organism begins in an egg. And the true life cycle of an organism is its life from egg through birth, growth and development, and maturity to the time it produces new organisms in the condition of eggs. The life cycle is from egg to egg. Birth and growth, two of the phenomena readily apparent to us in the life of every animal, are two phenomena in the true life cycle. Death is a third inevitable phenomenon in the life of each individual, but it is not a part of the cycle. It is something outside.

232. Life cycle of simplest animals.-The simplest animals have no true egg stage, nor perhaps have they any true

death. The new Amabæ are from their beginning like the full-grown Amaba, except as regards size. And the old Amaba does not die, because its whole body continues to live, although in two parts-the two new Amabæ. The life cycle of the simplest animals includes birth (usually by simple fission of the body of the parent), growth, and some, but usually very little, development, and finally the reproduction of new individuals, not by the formation of eggs, but by direct division of the body.

233. The egg. In our study of the multiplication of animals (Chapter VI) we learned that it is the almost univer

FIG. 142.-Eggs of different animals showing variety in external appearance. a, egg of bird; b, eggs of toad; c, egg of fish; d, egg of butterfly; e, eggs of katydid on leaf; f,egg-case of skate.

sal rule among many-celled animals that each individual begins life as a single cell, which has been produced by the