294 



NATURE 



[July 28, 1904 



vnaining half of {he book deals with the early histo- 

 genesis of the nervous system, and is practically a 

 recapitulation of the author's previous results, all, 

 however, carefully re-studied in the light of additional 

 material, and copiously illustrated with original 

 photographs. 



Apart from its scientific value, for which, indeed, 

 the author's name is a sufficient guarantee, the book 

 is a striking testimony to the debt neurology owes the 

 late Prof. His, for not only is the entire work, com- 

 prising practically all that is known of the develop- 

 ment of the human brain, based on the author's own 

 observations, but most of the facts here described owe 

 their first explanation to Prof. His. 



In the introduction, the author briefly describes his 

 methods, chief of which is his " graphic reconstruc- 

 tion," originally described by him in 1880, the only 

 difference being that photographs of serial sections 

 are now used instead of drawings. Following this 

 is a tabular statement of the embryos used, and a dis- 

 cussion of the difificulties of age estimation, and the 

 introduction closes with an earnest appeal for 

 •systematic measurements of all prematurely born 

 embryos at gynaecological institutions. 



The first portion of the book deals with the develop- 

 ment up to the close of the first month, and commences 

 with an account of the author's myelospongium, 

 which, in opposition to Koelliker, he believed to be a 

 ■syncytial network formed by the union of outgrowths 

 from the spongioblast cells. 



The author originally held that connective tissue 

 cells took part in the formation of the definitive 

 neuroglia, and especially that this was the mode of 

 origin of Deiter's cells ; in the present work, however, 

 he agrees with the majority of neurologists that the 

 original neural plate is alone concerned in the form- 

 ation of the supporting tissue. 



The author's " Keimzellen," as he showed in 1891, 

 form both nerve cells and glia cells, and, as Schaper 

 maintained in 1897, they are merely undifferentiated 

 ■cells of the myelospongium in active multiplication, 

 not, as the author originally supposed, a special form 

 ■of cell to be distinguished from all other cell-elements 

 .in the neural plate. 



The author gives a brief criticism of recent papers 

 in opposition to the neurone conception, on behalf of 

 which, it will be remembered, Prof. His was one of 

 ■the first advocates; in particular he deals with Bethe's 

 paper of 1903, in which the nerve is made to arise 

 from a linear syncytial cell series which also later 

 forms Schwann's sheath; His shows that Bethe is 

 really dealing with the mesenchymatous sheath, which 

 in the lower vertebrates, i.e. chick, appears very 

 early; in man, as His's photographs clearly show, 

 there is no possibility of confusing the growing end 

 of the non-medullated nerve bundle with the surround- 

 ing tissue, and especially is this the case with 

 Meynert's " fremdartiger " strands, as these grovif 

 into regions of the myelospongium practically free 

 from cells. This portion of the book closes with a 

 full description of the neural tube of an embryo at 

 the end of the fourth week, " Embryo N " already de- 

 scribed in previous papers. 



NO. 1S13, VOL. 70] 



The second portion of the book deals with the de- 

 velopment of the cerebral hemispheres, and commences 

 with a description of the author's well-known models; 

 this is followed by a detailed account of the histo- 

 genetic differentiation of the hemispheres up to the 

 close of the first month, and is illustrated by numerous 

 exceedingly clear photomicrographs. A few pages 

 follow on the blood vessels of the fore-brain. The 

 last twenty-five pages deal with the origin of the intra- 

 medullary tracts. 



. The whole book is written expressly for the pro- 

 fessed neurologist, and abounds in tabular statements, 

 references to individual embryos, and so forth ; but 

 there is much, especially in the earlier parts of the 

 book, which is also of interest to the student of general 

 morphology, and it is on behalf of such students that 

 we could wish the numerous excellent photographs of 

 brain sections had been provided with reference 

 letters. 



No bibliography accompanies the book, a want dulv 

 apologised for in the preface. It should also be noted 

 that, as indicated above, the whole development of the 

 brain is not dealt with; in the author's words, 



" Ich theile mit, was mir mehr oder minder 

 abgeschlossen vorliegt. Die Zwischenkapitel hoffe 

 Ich, falls mir Leben und Arbeitskraft bleiben, in 

 absehbarer Zeit zu konnen." 



All zoologists will regret that this hope is not 

 destined to be fulfilled. G. C. C. 



THE TURBELL.ARIA AS PARASITES AND 



PARASITE-CARRIERS. 



Die Turhellarien als Parasiten und Wirte. By L. 



von Graff. Pp. vi + 65. (Graz : Leuschner und 



Lubensky's Universitats-Buchhandlung, 1903.) Price 



14.50 marks. 

 pROF. VON GRAFF'S latest work dealing with 

 ^ the Turbellaria is no less interesting than any 

 of its predecessors, and students of parasitology must 

 stand greatly indebted to him for putting together in 

 such an accessible and stimulating form a full sum- 

 mary of all that is at present known of parasitism 

 amongst the Turbellaria. The first half of the work 

 is devoted to an account of the anatomy of six species 

 of parasitic rhabdoccels. Although all of these have 

 been previously described by von Graff himself, or by 

 other writers, the ampler accounts here given clear 

 up many doubtful points and supply precise infor- 

 mation not hitherto available on various anatomical 

 features. This part of the work is illustrated with 

 three plates of great excellence. 



The second part is devoted to considerations of a 

 more general character. It includes a list of all 

 known Turbellaria which liave adopted a parasitic 

 or commensal habit Amongst them von Graff dis- 

 tinguishes four principal grades of parasitism, namely, 

 (i) occasional commensalism ; (2) ectoparasitism ; (3) 

 occupation of some chamber in the body of the host 

 which communicates with the e.xterior ; and (4) endo- 

 parasitism. The author points out that the effects of 

 parasitism of the second and third grades do not pro- 



