July 28, 1904] 



NA TURE 



duce any very marked results on the parasite. The 

 development of organs of adhesion is not greater than 

 in the free-living species. Eyes may or may not be 

 present, and the size of the pharynx varies with the 

 species. The character shared by the largest number 

 of representatives of these groups appears to be the 

 loss of cilia, especially on the dorsal surface. There 

 is hardly an indication of that increase in size of 

 the genital glands so conspicuous in endoparasitic 

 forms where the eyes and adhesive organs are fre- 

 quently absent, the pharyn.x and nervous system much 

 reduced, whilst the body, on the other hand, is in- 

 variably completely ciliated. .As might be expected, 

 the number of families represented in grades (2) 

 and (3) is greater than the number of those which 

 contain endoparasites ; the majority of the latter belong 

 to the \'orticid£e. The hosts most affected by parasitic 

 Turbellaria are holothurians, Crustacea, and mollusca. 

 Other echinoderms, worms, tunicates, and vertebrates 

 are also preyed upon to a lesser extent. 



\'on Graff makes some interesting comments on 

 the classification of the platyhelminthes. The species 

 of the genus Temnocephala usually regarded as 

 transitional forms between the Turbellaria and 

 monogenetic trematodes might, he points out, be 

 referred with equal justice to the vorticid genus 

 Dero^toma. .Again, Fecampia, when sexually ripe, 

 agrees in characters of systematic importance with 

 the cestodes. In fact, " the more thorough our 

 knowledge of the platyhelminthes becomes, the 

 more difficult it is to define the classes of the 

 phylum. But just as so-called bad species are of 

 value to the student of evolution, so these ' bad 

 classes ' of the flat-worms supply him with arguments 

 which are the more convincing in that they rest on 

 the sure ground of ascertained morphological facts." 



The work concludes with a useful list of the very 

 numerous parasites with which the Turbellaria them- 

 selves may be infected. These range from symbiotic 

 algae and bacteria to trematodes and nematodes. It 

 is curious that the first recorded orthonectid, found by 

 Keferstein in Leptoplatia trcmellaris thirty-five years 

 ago, has not yet been adequately described. It differs 

 considerably from the other orthonectids noticed since 

 then. F. F. Laidlavj:. 



OUR BOOK SHELF. 

 Applii:atio)is of the Kinetic Theory to Gases, Vapours, 

 and Solutions. By W. P. Boynton, Ph.D. (New 

 York : The Macmillan Company ; London : Mac- 

 millan and Co., Ltd., 1904.) Price ys. net. 

 There are probably few mathematicians who can 

 follow the long and difficult investigations by which 

 it has been attempted to dispense with the second 

 law. and to represent thermodynamical properties of 

 matter as the changes which must necessarily take 

 ()lace in a molecular system for which the principles of 

 dynamics and the laws of probability are assumed to 

 hold good. Such attempts have been found practically 

 in every case to involve some jiirther assumption, 

 whenever a kinetic theory has been applied to the 

 consideration of irreversible phenomena, and Mr. 

 Burbury has unearthed this inevitable assumption 

 when it has escaped the attention of writers of several 



NO. 1813, VOL. 70] 



recent papers. It is probably as impossible to build 

 up an irreversible thermodynamical system out of 

 reversible d3'namical elements without any assumption' 

 as it is to build up a Euclidean geometry without some 

 axiom of parallels. 



But apart from such considerations as this, a 

 kinetic theory is of considerable use to the ordinary 

 physicist in furnishing him with a mechanical repre- 

 sentation of the properties of matter in its various 

 states. Dr. Boynton has taken as his standard the 

 requirements of a reader who is familiar with the 

 elements of the calculus, and he has produced a book 

 which will be of great value to students both of physics 

 and of chemistry. 



It is perhaps unfortunate that those English 

 physicists who are most competent to write books like 

 the present one are usually too much tied down by 

 other duties to undertake such work, especially as the 

 task is in most instances an unprofitable one to the 

 author. It is therefore satisfactory to find that Dr. 

 Boynton 's book is written so much on the lines of an 

 English text-book that it seems well suited for intro- 

 duction into this country. The features which we 

 particularly like are, firstly, that the author is careful 

 to give his readers no excuse for believing he has proved 

 a result when he has only given an elementarv in- 

 vestigation of it, and secondly, that instead of intro- 

 ducing irrelevant philosophical digressions or views 

 of his own, he has kept strictly to an exposition of 

 commonly accepted theories. 



It is much to be wished that the same could be 

 said of all the books which find their way into our 

 class-rooms from the other side of the water. It i& 

 because they do not generally come up to the present 

 standard of excellence that the difficulty of writing 

 English text-books that are worth writing is to be 

 regretted. G. H. B. 



Handbiich der Physik. By Dr. A. Winkelmann. 



Second Edition. First part of vol. iv., Electricity 



and Magnetism. 140 figures. Price 12 marks. 



First part of vol. vi., Optics. 170 figures. Price 



14 marks. (Leipzig : Barth, 1904.) 

 Every student of physics will share the satis- 

 faction of the editor of this treatise that a 

 second edition was called for so soon ; for he has 

 found it to be an indispensable storehouse of expert 

 knowledge in all branches of the subject, and the 

 need for another edition enables it to be brought once 

 more abreast of the rapidly advancing tide of know- 

 ledge. 



The book is of the nature of an encyclopaedia, for 

 each section is written by an expert in the section; 

 twenty-two of the leading physicists of Germany 

 collaborate in this way with Dr. Winkelmann, the 

 editor, in its production. Of the two parts before us, 

 that on electricity and magnetism is contributed by 

 Drs. Graetz and -Auerbach, while the part on optics 

 is the work of Drs. Czapski, von Rohr, and Eppen- 

 stein. 



References are brought up to the middle of 1902. 

 Thus amongst electrical instruments the Dolezalek 

 electrometer finds a place; the large amount of recent 

 work on the properties of dielectrics is very amply 

 discussed, including the double-refracting properties 

 for electric waves. Great stress is laid on the impor- 

 tant advances made in the construction and standard- 

 isation of standard cells. 



The optical portion is wholly occupied with geo- 

 metric optics and applications to optical instruments. 

 The fact that the writers are connected with the firm 

 of Zeiss is a sufficient guarantee of the quality of 

 their contributions. The only regret that one feels in 

 glancing through the book is that the tremendous 



