NA TURE 



25 



THE STUDY OF ANIMAL VARIATION. 



Materials for the Study of Variation, treated with 

 especial regard to Discontinuity in tlie Origin of 

 Species. By VV. Bateson, M.A., Fellow of St. John's 

 College, Cambridge. (London: Macmillan and Co., 

 1894.) 



MR. BATESON is to be congratulated on the com- 

 pletion of the first part of his work on variation 

 in animals, which treats of variation in the number and 

 position of organs forming parts of linear or symmetrical 

 series. Variation in the structure of such organs is only 

 partially dealt with, a fuller account being promised in 

 a future volume. The present work may be divided 

 into two parts — one purely descriptive, the other critical. 

 These require separate notice. 



It is impossible in a short space to give a proper 

 'account of the information brought together in the 

 ipurely descriptive part of the book. Mr. Bateson has 

 icarefully examined many of the principal European 

 icoUections, both public and private, and has in other 

 [ways collected a great store of original matter, which 

 jalone would make a respectable volume. In addition, 

 jhe has compiled a series of abstracts, containing the 

 lessentials of a large number of records made by others. 

 The labour expended upon the work of compilation alone 

 may be gathered from the list of authors referred to, 

 which contains some six hundred names. 



The facts recorded are grouped in numbered para- 

 ^T.iphs, on a system which makes reference to individual 

 cases easy ; the descriptions are for the most part admir- 

 able, and thev are supplemented, where necessary, by 

 adequate woodcuts. Full references are given, either to 

 the actual specim ns described, where such reference is 

 possible, or to the source from which descriptions are 

 [unted. 



The first twelve chapters deal with organs forming 

 oarts of linear series — such as the ribs, vertebne, or teeth 

 Df vertebrates, and similarly "repeated" structures in 

 other animals. In these chapters special attention is 

 irawn to cases of variation, such as the assumption by a 

 cervical vertebra of the characters proper to a dorsal 

 Vertebra ; and many remarkable examples of analogous 

 phenomena are given. For variation of this kind, in 

 which an organ in one region of the body is " made 

 ike" a serially homologous organ in an adjacent 

 'egion, the convenient word "homoeosis" is pro- 

 josed. Another interesting group of cases is described 

 IS showing that the number of specialised organs in a 

 series may be altered by a process of actual division, 

 iuch as that by which an increase in the number of 

 syes is effected in Planarians. 



The thirteenth and fourteenth chapters deal with 

 ncrease and reduction in the number of digits in the 

 vertebrate limb, and should be read in connection with 

 he twentieth ana twenty-first chapters, where closely 

 malogous phenomena, leading to duplication of arthro- 

 [)od appendages, are described. The wonderful relations 

 of symmetry, which are shown to hold in so many cases 

 NO. I2iSo, VOL. 50] 



between the "normal" and the "extra" limbs, have 

 been shortly described by Mr. Bateson on previous occa- 

 sions ; but the fuller statement here given forms perhaps 

 the most interesting portion of the book. 



The remaining chapters deal with variations in radial 

 series, such as those formed by many organs of coelente- 

 rates and echinoderms, and with cases which involve the 

 doubling of structures normally single, or the fusion in 

 the middle line of organs which are normally bilateral 

 and paired. 



Such in bare outline is the subject-matter of the 

 descriptive portion of the book. No quotation of 

 isolated passages is attempted, because no such pro- 

 ceeding could give an adequate idea of its importance. 

 The whole work must be carefully read by every serious 

 student ; and there can be no question of its great and 

 permanent value, as a contribution to our knowledge of a 

 particular class of variations, and as a stimulus to 

 further work in a department of knowledge which is too 

 much neglected. It is to be hoped that Mr. Bateson 

 will not rest content with his already great achievement, 

 but will proceed with his promised second volume, 

 which will be eagerly looked for by those who read 

 the first. 



If the criticism and enunciation of opinions had been 

 performed with the same care as the collection of facts, 

 the commentary which runs through the book would have 

 gained in value, and several inaccuracies, due partly to 

 want of acquaintance with the history of the subject, 

 would have been avoided. The only contention which 

 can here be noticed is that alluded to on the title-page, 

 namely that variation frequently proceeds in such a way 

 that changes in an organ occur only by steps of definite 

 and measurable magnitude ; and that discontinuous 

 variation of this kind is necessary for the evolution of 

 new species. In Mr. Bateson's words : 



" The first question which the study of variation may 

 be expected to answer, relates to the origin of that dis- 

 continuity of which species is the objective expression. 

 Such discontinuity is not in the environment ; may it not, 

 then, be in the livmg thing itself.^" 



The statement that discontinuity is not in the en- 

 vironment, is justified as follows : 



" Here then we meet with the difificulty that diverse 

 environments often shade into each other insensibly, and 

 form a continuous series, whereas the specific forms of 

 life which are subject to them on the whole form a dis- 

 continuous series. . . . Temperature, altitude, depth of 

 water, salinity, in fact most of the elements which make 

 up the physical environment are continuous in their 

 gradations," and so on. 



Here the reference is only to the physical conditions 

 which form a part of the environment affecting animals. 

 That these physical conditions do oftenforma "continuous 

 series" is no doubt true, although it is also true that in a 

 large number of cases they do not. But Darwin, Wallace, 

 and the greater number of subsequent writers on the 

 doctrine of natural selection, agree in believing that the 

 most important part of the environment against which a 

 species has to contend consists of other living things. 

 This view is dismissed in the following short foot-note : 



" It may be objected that to any organism the other 

 organisms coexistmg with it are as serious a factor of the 



