146 



NATURE 



[June 14, 1906 



The fifth volunif, wliirh deals; with our knowledge 

 ■of the pineal body, and the pineal eye or parietal 

 organ, was entrusted by Prof. Oppel to the safe 

 hands of Dr. F. K. Studnicka. That authority has 

 not only coordinated the results contained in some 

 three hundred papers dealing with this structure, but 

 has added much new and valuable work of his own. 



The study of structure by itself and for itself is a 

 most unprofitable occupation, and Prof. Oppel, by 

 Including a free reference to function and develop- 

 ment, has not only added greatly to the interest, but 

 also to the value of these two volumes. 



A. K. 



A TEXT-BOOK OF GENETICS. 



Vorlesiingen uber Deszendenztheorien mit besoiiderer 



Beriicksichtigiing der Botanischen Seite der Fragr. 



gehaUen an der Reichsuniversitdt zu Leiden. By 



Dr. J. P. Lotsy. Erster Teil. Pp. xii + 384. 



(Jena : Gustav Fischer, igo6.) Price 8 marks. 

 A S the moment is favourable, may it be suggested 

 ■•' » that the branch of science the rapid growth of 

 Avhich forms the occasion of Prof. Lotsv's book 

 ■should now receive a distinctive name? Studies in 

 ^' Experimental Evolution " or in the " Theorv of 

 Descent," strike a wrong note; for, theory apart, the 

 physiology of heredity and variation is a definite 

 branch of science, and if we knew nothing of evolu- 

 tion that science would still- exist. To avoid further 

 periphrasis, then, let us say genetics. 



Prof. Lotsv's lectures are a welcome contribution 

 to genetics. They are expository and critical rather 

 than creative, but there is plenty of room for such a 

 work. Since it must be admitted that to most of us 

 facts appeal " first when wo see them painted," such 

 a presentation as this book provides should attract 

 many who would find little to detain them in original 

 records. 



There are twenty lectures in this first part, and a 

 second part is promised. After a philosophical intro- 

 duction, which must be left to the judgment of those 

 versed in such matters, the author proceeds to a care- 

 ful discussion of the evidence for direct adaptation. 

 1 hough no Lamarckian in the usual sense, he has a 

 high respect for Lamarck's penetration and breadth of 

 view. In this revindication of a great name, 

 naturalists of the younger generation who have studied 

 Lamarck's writings at first hand will probably 

 sympathise with Prof. Lotsy. In a limited sense the 

 modification produced by environment — biaiometa- 

 morphosis, as Prof. Lotsy calls it — is important. No 

 botanist doubts that the forms of plants can be pro- 

 foundly changed by the conditions to which they are 

 exposed. The normal or habitual form in which we 

 know a species is only one of these modifications. 

 Consequently each experimental proof of the depend- 

 ence of form on environment has a direct bearing on 

 the genesis of type. But the question of purposeful 

 or adaptative modification is quite distinct, and of any 

 transmission of purposeful modification in descent 

 there is no evidence. 



The section of the book which gives it its chief 

 NO. 191 I, VOL. 74 j 



value is that in which an account is provided of the 

 new developments in genetics, especially Mendelian 

 analysis and the experiments of de Vries. The conse- 

 quences of Mendelian segregation are described with 

 great clearness, and are illustrated by some excellent 

 diagrams, of which one (p. loi) is striking and novel. 

 The members of the various generations are shown 

 in a perspective view, drawn approximately to scale, 

 in a way which should do something to remove the 

 supposed obscurity of these phenomena. Both the 

 description of the facts and the critical discussion of 

 the bearing of Mendel's discovery on the earlier or 

 Galtonian method of calculating inheritance are 

 especially lucid and to the point. 



The weaker features of this section are such as are 

 almost inevitable in attempts to confine a rapidly 

 growing study within text-book limits. The relative 

 importance of the various elements is continually 

 changing. For example, though due stress is laid on 

 Tschermak's fine series of cases illustrating the influ- 

 ence of hidden factors, or cryptomeres, Cu^not's useful 

 exposition of the part played by double factors in the 

 case of mice seems to have been left out. Having 

 regard to the remarkable developments which have 

 followed, this omission is unlucky. In the same con- 

 nection it is a matter of special regret to myself tRat 

 the revised and simplified account of the " walnut " 

 combs in fowls did not reach Prof. Lotsy in time to 

 prevent a reproduction of my former and erroneous 

 idea in his text-book. 



By all who are working at genetics the discussion 

 of de Vries' mutations will be read with interest. Till 

 now those remarkable observations have been regarded 

 either with indiscriminate enthusiasm, or with still 

 more unreasoning suspicion. But on those who know 

 that the mutations of CEnothera are not errors of ob- 

 servation, and hesitate to accept them as the single key 

 to the final mysteries of evolution, the question begins 

 to press: What are those mutations? Upon this 

 point the teaching of genetic research is clear. Before 

 we can form a definite view as to the nature of anv 

 given mutation we must know its gametic relations 

 to the type from which it sprang, and to the sister- 

 mutations. So far, these relations, as expressed by 

 the ratios in which the forms appear, seem to be 

 almost always irregular in the CEnothera cases. Ex- 

 perience, however, has shown that such irregularities, 

 as in the case of Miss Saunders' Matthiola, may con- 

 ceal an underlying regularity which fuller anatysis can 

 reveal. For instance, we know that various individuals 

 of a form A may give respectively an F„ ratio 

 9A : 7B ; or ^A : iB ; or all A ; or 27A, qC, 28B, and 

 so on, and the causation or meaning of these several 

 ratios is clear. May not such complexities be the 

 source of the confusion which apparently besets the 

 CEnothera cases? That is the opinion to which Prof. 

 Lotsy inclines, and the position is for the most part 

 unassailable as yet. .\11 that can be positively asserted 

 is that these mutations are forms arising discon- 

 tinuously, and that their distinctions are exactly com- 

 parable with those that often appear to characterise 

 species. But now that we understand what a medley 

 of phenomena is included in the term " specific 



