I50 NATURAL SCIENCE. apr,,.. 



however, is no defect ; on the contrar}-, the variations make the hook 

 more interesting. A dull monotony is avoided in this way, and also 

 by a frequent change of type, and the interpolation of tabular 

 comparisons of animals. The style, moreover, is attractive — a state 

 of affairs not often found in text-books. 



Mr. Thomson retains the division Worms, though he distinctly 

 states that " the animals included . . . form a heterogeneous mob, 

 with little in common." The expression " Worms," when used, is 

 almost invariably written between inverted commas, which further 

 emphasises tliis perfectly just objection to the retention of such a 

 group. 



Two hundred and thirty-four pages out of a total of six hundred 

 and four are devoted to the Vertebrata, not inchiding Aviphioxus, 

 Balanoglossvs, and the Tunicates. This seems to us to be rather out 

 of proportion, though in most text-books the \^ertebrata claim an 

 equally large share of the author's attention. One of the few books 

 in which they are treated justly, but with no favour, is Professor 

 Gegenbaur's well-known work. 



Nearly ever}' page has interesting notes about the habits of the 

 animals under consideration. Thus, in describing the Spiders, Mr. 

 Thomson does not forget that their webs are rivalled in fineness by 

 Mr. Boys' quartz fibres ; and he gives some account of the remark- 

 able observations on the "courtship" of the creatures by Mr. and 

 Mrs. Peckham, partly because " it affords a pleasant interlude in our 

 systematic survey," but also as a peg whereon to hang comments on 

 the theory of " Sexual Selection." Most, if not all, of the current 

 generalisations of Biology and the theories which have been put 

 forward for their explanation are treated of ; and some of these are 

 interspersed among the chapters upon the various groups, as in the 

 instance mentioned. The general facts of Physiology, Histology, 

 &c., occupy the first ninety pages of the book. Evolution has a short 

 chapter of nine pages to itself. 



Though the theories most in vogue are impartially stated, we 

 notice frequent indications of the author's own vicAvs. These are by 

 no means obtruded on the reader ; indeed, the faith of the student in 

 the orthodox theories will not be rudely shaken, even if a little doubt 

 is occasionally infused into the complacent attitude produced by the 

 teaching of most professors and lecturers. In treating of Sexual 

 Selection, Mr. Thomson is inclined to lay more stress upon "the 

 fundamental (jualities of maleness and femaleness," than any selection 

 by the female, a position taken up by Professor Geddes and himself 

 in their " Evolution of Sex." He remarks that " it is difficult to 

 understand how this characteristic smallness [of the malesj, though 

 perhaps advantageous and likely to be favoured by natural selection, 

 could be entailed on the male offspring only." Much harder to 

 understand is sexual trimorphism, such as occurs in certain butter- 

 flies. We have cases where an insect has two kinds of females, one 

 more or less like the male, the other " mimicking" another butterfly, 

 supposed to be protected by a disagreeable taste. 



The book is, in fact, to be decidedly recommended, not only to 

 students preparing for examinations, but to persons already possessing 

 a certain amount of knowledge of the subject, who desire to have the 

 main facts of Zoology compressed into a single thoroughly readable 

 volume. The only parts of the book with which we find fault are the 

 illustrations ; and this not on account of want of clearness, but from 

 their inartistic style. They are roughly executed outline drawings 

 arranged on thirty-two plates. 



