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 G. J- ROMANES'S MEXTAL EVOLUTION IX AXIMALS. 29-5 written above one another to express the exact degree of intelli- gence at which various classes of animals have arrived are some- times the names of processes that are common to a large number of particular mental acts (as ' Memory,' ' Association by Con- tiguity,' 'Association by Similarity,' 'Reason'), sometimes names of special acts or of concrete products of mental activity (as ' Kecognition of Offspring,' ' Dreaming,' ' Understanding of Mechanisms'). This mixture of terminologies having different values is a little incongruous. The scale of emotional develop- ment seems to have been drawn up without any attempt at a preliminary analysis of the emotions, and is so far more consistent than the scale of intellectual development, which is the result of a compromise. ' Pleasures and Pains ' seem out of place among 'Products of Intellectual Development'. And although in the chapter on Emotion Dr. Romanes says that the emotions are represented as originating at the same time as perception because "as soon as an animal or a young child is able to perceive its sensations, it must be able to perceive plea- sures and pains," no use is made, in his discussion of the emotions, of the theory of pleasure and pain adopted by him from Mr. Spencer and Mr. Grant Allen. It is in his detailed treatment of Instinct, extending to eight chapters (pp. 159-317), that the author makes the most decided advance. Other writers have for the most part treated some one factor in the formation of Instinct in isolation from the rest. Dr. Romanes has brought together the ideas of "Primary In- stincts " that originate by natural selection, and of " Secondary Instincts" that are the result of the transmission of organised habits. He has explained how the two processes by which instincts have been formed may influence one another, and how intelligence may modify instincts formed by each process and by the combination of both. These ideas are developed with great elaboration. All the positions that are taken up as to the j existence of the simple processes, as to the compounding of 1 factors, and as to the transmission by heredity of modifications j of instinct are established by evidence. A good view of the general result of this investigation is given by the diagram placed i opposite p. 265. The posthumous Essay by Darwin printed as an Appendix is i chiefly a collection of facts bearing on the theory of Instinct ; ! and other notes made by the great naturalist are used by Dr. ! Romanes in his own treatment of the subject. No completed , theory is to be found in the Essay ; but it will have some interest
 * for those who may wish to study in an earlier stage thoughts

that are fully worked out in the eighth chapter of the Origin of THOMAS WHITTAKER.