March, 1913. 



KNOWLEDGE. 



119 



pulse theory. But these arguments all appear to be based 

 on the assumption that the ionising power of the 7 and X-rays 

 is entirely due to their conversion into £ rays, the latter 

 being alone responsible for the ionisation. The experimental 

 evidence offered for this assumption, however, seems some- 

 what inadequate. 



H. S. Redgrove. 



ZOOLOGY. 



An Introduction to the Study of the Protozoa. — By E. A. 

 Minchin, F.R.S. 517 pages. 194 illustrations. 8$-in. X5j-in. 



(Edward Arnold. Price 21/- net.) 



The recognition during the last decade or so of the extreme 

 importance of the part played by the lowest of all animals in 

 the economy of nature — and more especially as regards man 

 himself — has led to the Protozoa being studied with an amount 

 of labour and zeal never, perhaps, accorded to any other 

 group of animals. And among those who have laboured 

 hardest in this productive field is the author of the volume 

 before us, who, with the true modesty of a great investigator, 

 claims for his work only the position of an introduction to the 

 vast subject he has made his own, and that it is not to be 

 regarded as a complete treatise. To set forth all that is 

 already known concerning the Protozoa would, he says, 

 require a work many times as large. That the present volume 

 is not intended for amateurs, goes without saying ; its aim 

 being to supply students who have at least some general 

 knowledge of biology, with a means of taking up the study of 

 the Protozoa in real earnest. How important to the biologist 

 is this study may be gleaned from the single fact that, apart 

 from all other considerations, it throws " great light on some 

 of the fundamental mysteries of living matter — as, for example, 

 sex." 



In so wide a field it is essential to concentrate attention on 

 particular aspects of the group, and Professor Minchin has, 

 therefore, very wisely laid especial stress on the parasitic 

 forms, both on account of the biological problems they present 

 and of their intimate association with the practical needs of 

 human life. The medical aspect of parasitic protozoans is, 

 however, very properly left to the doctors, who are furnished 

 by the author with a solid basis of fact upon which to work. 

 In his concluding chapter, the author gives some most in- 

 teresting speculations with regard to the origin of the Protozoa 

 and the types which should be regarded as most closely 

 approximating to the ancestral stock. In his opinion the 

 nearest approximation to that stock would be " a minute 

 amoebula-form, in structure a true ceil, with nucleus and 

 cytoplasm distinct, which moved by means of pseudopodia." 

 To all workers on the subject Professor Minchin's volume is 

 absolutely indispensable. ., . 



The Childhood of Animals. — By P. Chalmers Mitchell, 

 F.R.S. 269 pages. 36 illustrations. 12 plates. 9i-in. X6i-in. 



(Wm. Heinemann. Price 10/- net.) 



The subject of which Dr. Mitchell treats in such a fascinating 

 manner in this volume is to a great extent untrodden ground, 

 for although we all know that caterpillars change into butter- 

 flies and moths, and tadpoles into frogs and toads, while the 

 young of many species of mammals differ to a greater or less 

 extent from their parents in the matter of colouring, yet the 

 meaning of these changes and the purposes of youth have 

 never previously, we believe, been discussed in the thoughtful 

 and thorough manner characteristic of the present work. The 

 basis of the work was a course of lectures delivered by the 

 author to a juvenile audience, at the Royal Institution, during 

 the Christmas season of 1911-12; and although the work itself 

 is not a printed version of the discourse, yet it tells the same 

 story, although in a somewhat different and fuller fashion, 

 more adapted to the requirements of adult readers. Although 

 the work makes no pretence to be a complete treatise on 

 such a wide subject, yet it covers a great deal of the 

 ground, and records a very considerable proportion of 

 published observations relating to that period of the life 



of animals intervening between birth and maturity. To 

 review the volume in detail is not possible within our 

 limits of space ; and we can, therefore, only refer to a few 

 interesting points. In the chapter on the duration of youth 

 in mammals, it is pointed out that this period is longer among 

 the more civilised than among the lower human races, and 

 that in the former it appears to be still increasing in length. 

 In rhinoceroses, horses, and tapirs the length of the duration 

 of youth appears to vary according to the bodily size of 

 the animals ; and the same also holds good among ruminants, 

 in which, however, owing to the advanced stage of develop- 

 ment of the young at birth, the period of youth is unusually 

 brief. Much interesting information is to be found with 

 regard to the colour-patterns of young mammals, as contrasted 

 with those of their parents. In mammals, the author believes 

 that spots were the primitive type of colouring, and that these 

 are connected with the tesselated nature of the skin. These 

 spots mav expand into short stripes, or coalesce into longer 

 longitudinal or transverse stripes, which undoubtedly help to 

 render the animals inconspicuous, although this is not the 

 cause of their development. A uniform coat, which so often 

 replaces the spots or stripes of the young, but may occur in 

 the first dress of the latter, is apparently a specialised develop- 

 ment ; and the same seems to be the case when vivid patches 

 of colour, which do not correspond with structural differences 

 in the body, replace the first coat. In the latter case the 

 object of the pattern, which, unlike the retention in the adult 

 of a juvenile spotted coat, is generally more pronounced in 

 males than in females, may serve, by breaking up the outline 

 of the body, for concealment. 



The book should be studied by all naturalists, as well as by 



the general reader. 



R. L. 



Elementary Entomology. — By E. D. Sanderson and 

 C. F.Jackson. 372 pages. 476 illustrations. 8-in. X5f-in. 



(Ginn & Co. Price 8/6.) 



The writers of this well-illustrated volume, who are pro- 

 fessors and lecturers in American science colleges, have 

 found by experience that no text-books on entomology have 

 sufficed for their needs ; and they accordingly endeavoured 

 to produce one which shall meet the requirements of both 

 elementary students and their teachers. In this, so far as we 

 can judge, they appear to have attained a high degree of 

 success; for the book, without being unduly technical, conveys 

 a good idea of the anatomy, life-history, and classification of 

 insects, and this, too, in a relatively small space. Of especial 

 value are the " keys" to the important families of the various 

 orders of insects, which are evidently drawn up with great 

 care, and the meaning of which is in many instances made 

 plain by the aid of explanatory diagrammatic illustrations. 

 The dominant note of the book is, as might have been 

 expected, the economical aspect of the subject ; for the old- 

 fashioned cabinet entomology is, at least to a great extent, 

 dead and buried, and the modern cult devotes itself to the life- 

 histories of insects, and their role as carriers of infection to 

 man and animals and their injuries to live-stock and crops. 

 The authors, however, very wisely insist that an adequate 

 knowledge of really useful economic entomology cannot 

 possibly be acquired merely by a more or less casual study of 

 the common injurious insects ; and they have accordingly 

 produced a work which should enable every student to obtain 

 a thorough mastery of the elements of the subject. R , 



The Evolution of the Vertebrates and Their Kin. — By 

 W. Patten. 486 pages. 309 illustrations. 9-in.X6J-in. 



(J. & A. Churchill. Price 21/- net.) 



In this handsome volume Dr. Patten, Professor of Zoology 

 at Dartmouth College, Hanover, N.H., records his endeavour 

 to solve one of the greatest and most difficult problems with 

 which biologists are now confronted. As he remarks, 

 vertebrates suddenly make their appearance in the geological 

 record at the close of the Silurian or the commencement of 



