NA TURE 



437 



THURSDAY, MARCH 7, 1901. 



THE PRESENT ASPECT OF SOME 

 CYTOLOGICAL PROBLEMS. 



The Cell in Development and Inheritance. By E. B. 

 Wilson, Ph.D., Professor of Zoology, Columbia Uni- 

 versity. Second edition, revised and enlarged. Pp. 

 xxi + 483. (New York : The Macmillan Company. 

 London : Macmillan and Co., Ltd., 1900.) Price 14^'. 

 net. 



DURING the few years which have elapsed since the 

 appearance of the first edition of Prof. Wilson's 

 book on the cell, the rapid accumulation of new facts has 

 resulted in the modification, in many important respects, 

 of the views which were entertained concerning many 

 cell phenomena even so lately as five years ago. Hence, 

 though the volume before us is issued as a second 

 edition, it has not only been considerably enlarged, but 

 also much of the original matter has been displaced to 

 make room for new treatment which shall more faithfcilly 

 reflect the attitude of cytologists towards the problems 

 which confront them at the present time. And we may 

 fairly say that the author's efforts have not only been 

 largely successful, but they have resulted in the produc- 

 tion of one of the best works which it has been our good 

 fortune to meet with for a long time. 



The whole subject is handled in an easy and masterly 

 fashion, and the reader is enabled readily to grasp the 

 leading facts and to obtain a clear insight into the nature 

 of the chief questions of cytological importance. Of 

 course the book is not without its faults, but they are not, 

 for the most part, serious ones. The author is naturally 

 less at home when dealing with botanical than with 

 zoological work, and indeed he says as much in his 

 preface ; but we notice, here and there, slips which might 

 have been easily avoided. Amongst the most obvious of 

 these is a somewhat misleading account of the mor- 

 phology of the embryo-sac on pp. 264-5. ^ more trifling 

 matter is the rather irritating recurrence of eulogistic 

 adjectives, and the reader is apt to weary of a " brilliant " 

 hypothesis or an "interesting" observation which is 

 shown a few lines farther on to be untenable or 

 unsound. 



The volume opens with a brief historical introduction, 

 in which it is satisfactory to find that to Cohn is given 

 the credit, which undoubtedly belongs to him, of having 

 been the first clearly to identify sarcode with protoplasm. 

 Then follow chapters on the division of the cell and the 

 nucleus, and of the more intimate structure of the cell- 

 constituents. In the account of the details of karyo- 

 kinesis, a fairly representative series of examples is given ; 

 but we could have been well contented had the author 

 seen fit to amplify his treatment of the simpler and more 

 primitive forms of life, seeing that so many of them 

 exhibit remarkable and suggestive deviations from the 

 course of events as pursued in the higher animals and 

 plants. 



Prof. Wilson deals with the vexed questions which 

 have arisen concerning the centrosome in a cautious and 

 NO. 1636, VOL. 6i\ 



discriminating manner, and he discusses the various 

 theories which have been put forward respecting the 

 nature and functions of this highly enigmatical body. A 

 considerable mass of evidence has been gradually accu- 

 mulating which tends to show that a greatly exaggerated 

 importance has been assigned to it by many investigators. 

 There are instances in which it can only be recognised 

 as a transitory structure which persists during special 

 phases of activity, to disappear when these subside. The 

 view was at one time current amongst the majority of 

 cytologists that the centrosome represented a permanent 

 structure which presided over the divisions of the 

 nucleus, and that it was, in fact, par excellence the organ 

 which aroused and directed the karyokinetic processes. 

 More extended investigation has, however, failed to sup- 

 port this proposition, and in not a few cases, especially 

 amongst the higher plants, there is no good evidence of 

 the existence of a centrosome at all. Furthermore, the 

 researches of Hertwig, Morgan, and especially the recent 

 ones of Loeb, have proved that eggs in which the original 

 centrosomes have undergone complete degeneration are 

 yet capable of exhibiting the entire processes of division 

 when appropriately stimulated, and this without the 

 entrance of a sperm or any other centrosome-bearer 

 whatsoever. 



The question as to the permanence of the chromo- 

 somes is also considered, and, on the whole. Prof. Wilson 

 appears to incline to the view that the same chromo- 

 somes which were visible in the daughter nuclei at the 

 close of a division reappear when the latter proceed to 

 divide once more. In conformity with this idea, he sup- 

 ports the hypothesis that in cases where less than the 

 normal number of chromosomes arise in a nucleus, these 

 are in reality plurivalent- — that is, each apparent chromo- 

 some is compound, and represents two (or more) true 

 chromosomes united together, although their individuality 

 may be for the time entirely masked. Thus it is well 

 known that the nuclei of both the ovum and the spermato- 

 zoon possess only half the number of chromosomes 

 characteristic of the somatic cells of the organism, and 

 that this "reduction" is accomplished in connection with 

 two peculiar and rapidly-succeeding nuclear divisions. 

 Each of these chromosomes (at least in the first division) 

 is then regarded as plurivalent (bivalent) — that is, as 

 composed of, at any rate, two individuals which have 

 not separated from each other. One necessary con- 

 sequence of this view is that somewhere during one 

 of these divisions, or at any rate before the forma- 

 tion of the sexual cells which arise from them, there 

 must be a qualitative distribution of the real primary 

 chromosome-individuals between two nuclei. Such an 

 occurrence was regarded as antecedently probable by 

 Weismann, and his views received a remarkable con- 

 firmation at the hands of several investigators, who de- 

 scribe the sequence of events as proceeding in a manner 

 such as to render it apparently clear that a qualitative 

 distribution does actually occur. 



On the other hand, many others have been unable to 

 find any evidence for the existence of such a type of 

 division in other organisms, and conclude that the facts 

 are strongly opposed to it. Should their view be correct, 

 even in the case of a single example, the whole objective 



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