ANIMAL LIFE AND EVOLUTION.*

MESE two books deal with animal life from different aspects. One treats of the growth and evolution of the individual, the other of the evolution and growth of forms or species. It must not be thought that Dr. Chalmers Mitchell's Child- hood of Animals is a mere reprint of a shorthand note of his lectures to children at the Royal Institution. But perhaps the fact that the book is based on spoken lectures * (1) The Childhood of Animals. By P. Chalmers Mitchell, M.A., LL.D., D.Sc., F.B.S. With coloured plates by E. Yarrow Tones, XL, and drawings by B. S. Brook-Greaves. London : W. Heinemann.[10s. net.]—(2) Toe Illroloth of Groups in the Anima/ Kingdom, By B. E. Lloyd, ALB., D.Sc. (Load.). With two coloured plates, London: Longasaus and Co. (As. net.)

may explain and excuse a certain amount of diffuseness and repetition. Embryology, as everyone knows, has added much to our knowledge of animal descent and relation- ship. Childhood is an unbroken continuation of the embryo stage, and it might well be expected that a careful study of animals between birth and maturity would prove instructive.

Nor on the whole are the results disappointing. Dr. Chalmers Mitchell's book is written with a notable absence of techni- calities, and can be read and understood by anyone who likes animals. His attitude is scientific and not sentimental ; he brings to bear on his subject the great reading and retentive memory of a trained zoologist; and, above all, he has a wide

and rare menagerie experience. His pages are enlivened with personal anecdotes. Mr. Yarrow Jones has contributed some effective and original coloured plates, whilst Mr.

Brook-Greaves has added a number of clever pencil drawings

which are a welcome change from photographs. All the elements of a pleasant and interesting book are therefore present, and such it will be found by every naturalist.

Some animals have no youth. "It is the more intelligent animals that have the longest period of youth." This theme Dr. Chalmers Mitchell enlarges on, and he surveys the duration of youth, the brood-care, the provision of food, in a great number of mammals, birds, reptiles, and a few of the lower

invertebrates. With the prolongation of youth comes, invari- ably, the limitation of families. A turbot produces fifteen million eggs in a season; an elephant lives a century and does

not give birth to more than six young. Death falls most heavily on young animals—their destiny is to be eaten by

others. They are more succulent and easier to catch. So as families become smaller, parents have to devote themselves to their young lest the race become extinct. We have said that some animals have no youth : these are the one-celled protozoa which increase by division and make it hard to decide which

is daughter and which mother. Among higher animals, which are composed of many cells, one may distinguish two groups. First, those in which the young always resemble the parents more or less closely. The young of nearly allied animals are more alike than the adults. The simian characters of new-horn children are always an amusing and a fertile theme. In the second group we have some vertebrates and many in-

vertebrates which pass through a larval stage in which they are totally unlike their parents. The tadpole, which becomes a frog, starts life as a fish. The fly arises from a maggot or gentle.

"The changes through which many of these creatures pass on their way to adult life are as strange as if a new-born human baby were to have the form of a fish, swimming in a tank, feeding greedily on worms and water-fleas, and then after a few weeks or months were to grow very fat and sleepy, to split along the back, and discarding its fish-skin, to creep out on land in the form of a hedgehog ; and if the hedgehog were to live for months or years the life of a humble quadruped, growing bigger and fatter until it, too, reached a limit of growth, broke out of its hedgehog skin and appeared as an adult human being fitted in body and mind to be a bishop or a burglar."

There are also other animals in which the promise of youth is not fulfilled by the maturity of age. An active tadpole, which seems on the road to develop a backbone, fixes on a rock and ends as a stationary and contemptible sea-squirt. The sedentary barnacle is a degenerate crab or crustacean. These aspects of youth, which are so strangely contrasted, do not agree with any systematic classification of animals. The rabbit is born naked and helpless ; the hare is active and maturely clothed. The youth of animals, from man and the great apes down to water-fleas and earwigs, the taming of young animals, and, lastly, the purpose of youth, afford an endless and attractive subject for Dr. Chalmers Mitchell. There are many anecdotes scattered through these pages of a tame caracal, now dead, and a tame hyrax in the possession of the author—the hyrax, which is the Biblical coney, is, as we all know, "exceeding wise "; but the grounds which induce the author to form this conclusion are different from those which

affected the opinion of the Scriptural writer. Dr. Chalmers Mitchell has a great horror, which many share, of performing animals bullied into making themselves ridiculous on a music-

hall stage.

Lastly, it is time to inquire into the purpose of youth, which possibly may direct us on the true path in the education of the young. During youth primitive instincts are modified by experience. But there is no complete separation between instinct and experimental action. Animals which are ruled iy instinct come into their fell powers at ones and have little

'o gain by-experience. •

"-fn the vertebrates, however, and especially and increasingly to in vertebrates:with high development, the rigid instincts are being broken down and replaced by actions-controlled by experi nee and by, memory, and so fitting more varied circumstances and 'note varied environment. ' The" period of youth is prolonged to t.fford time for this. The animals are protected and cared for by heir parents, and allowed a space in which the burden of life Ines not press heavily upon them, and in this time they have to -lucate their instincts, destroy their rigidity, allow them to be .ontrolled by the stored-up results of experiment. The purpose

■ f youth is to give time for this, and. therefore thoseanimals which re most intelligent, which have, the most complex brains, have he longest period of youth."

'he secret of taming -young wild animals is to get them to -render to a human being the confidence and love they give

-e their mothers. All who have brought np young birds will eppreciate the-meaning of-this. So young ungulates naturally follow and young carnivores are accustomed to be carried and rolled on the floor. But rodents, of kinds that are not carried, and monkeys, which cling to their mother, will always be apt to bite when they- are seized and lifted. So, too, it is hopeless ever to expect arboreal animals to become what German trainers call Stubenrein.

It is unlikely that anyone who reads Dr. R. E. Lloyd's title, The Growth of Groups in. the Animal Kingdom, will guess the scope and purport of his book. It is the work of a

thoughtful writer, and will stimulate thought among those who read it. Dr. Lloyd is a naturalist in the Indian medical service, and he tells us that his aim is to lessen the belief in

natural selection as a creative agency." He is too wise to be led into any definition of a species which is a conventional and not a real group. He shows that the only real unit is the individual, and that either obvious or microscopic differences between, individuals can always be pointed out. The • syatematist declares that they are not constant variations.. Dr.. Lloyd's mind has evidently been greatly influenced by the facts established by Mendel and De Vries. He is, to put it shortly, a " Mutationist." " The specific character of a mutant or true species is a single indivisible attribute, affecting the whole constitution of an organism, having noparts such as might appear separately in different individuals.'.' De Vries regards the specific quality to be the expression of a single unit character. Varietal characters, on the other hand, affect only .a single part of the organism. Whether there is or is not this fundamental distinction between what Darwin called continuous and discontinuous

variation, is, of course, one of the great problems of biology. During the plague investigations in India enormous numbers of rats passed through Dr. Lloyd's hands, and he studied this material. He uses.the facts he observed, and also Tower's well- known and extensive observations on the races of potato-beetle in America, as an argument in favour of the appearance of new

species as sudden mutants. He even suggests that a demented person is a mutant, but one with no chance of surviving. But i f we have followed Dr: Lloyd's argument. and it is a careful and an interesting one, it may well be that he is right in believing that species originate as sports in nature. It does not, how- ever, seem to us to follow that the work of natural selection is thereby to be depreciated. Big variations may have a greater survival value than small. It may work on discontinuous as well as on continuous variations. Darwin inclined to the latter view, but he had not before him, unfortunately, the work of Mendel, De Vries, and their numerous modern followers. Be this as it may, Di. Lloyd's is a stimulating and; in some respects, novel statement of the evolution problem. Ap- parently he regards natural selection and theological anthropomorphism- as attempts to explain the unknowable. But what is meant by explain? Nothing is ever really ex

plained completely.