NATURE 



H5 



THURSDAY, DECEMBER 17, 1891. 



TWO ZOOLOGICAL TEXT-BOOKS. 



Text-book of Comparative Anatomy. By Arnold Lang, 

 Professor of Zoology in the University of Ziirich. 

 ' Part I. Translated into English. (London: Macmillan 

 and Co.) 



Lehrbuch der vergleichenden Entwickelungsgeschichte 

 der Wirbellosen Thiere. Von Dr. E. Korschelt und 

 Dr. K. Heider. Parts L and II. (Jena : Fischer.) 



THERE can be no doubt that the first-named of these 

 two treatises, containing, as it does, a number of 

 new engravings and process-cuts, and a recognition and 

 exposition of some of the recent advances in zoological 

 science relating to Invertebrata, will be useful to junior 

 students in our Universities. 



Whilst it will, no doubt, fulfil the author's purpose, and 

 have a measure of success in its original German form, 

 I must confess that it does not appear to me to be 

 altogether satisfactory, whether we view it as an element- 

 ary sketch for junior students or as a work designed to 

 assist the serious devotee of zoological research. 



The most serious defect in the book from the latter 

 point of view is that no attempt whatever is made to refer 

 a given statement to the author who is responsible for it. 

 A very short bibliography is appended to each chapter, 

 but the reader of the book receives no assistance in 

 tracing a new or striking observation to an original 

 source. This curious reticence as to original authorities 

 is carried to an extreme. For instance, on p. 137 there 

 is a brief description (without figures) of Cceloplana and 

 Ctenoplana ; Korotneff is alluded to anonymously as " the 

 discoverer of Ctenoplana " ; neither his name nor that of 

 Kowalewsky, the discoverer of Cceloplana, are mentioned ; 

 and the student has no means afforded him, either 

 through the text or through the scanty bibliography, of 

 finding out anything more as to these two remarkable 

 forms. The same defect characterizes every page of the 

 book ; a very little trouble would have sufficed to remedy 

 this, and thus not only to make the book useful to 

 students but also to do justice and honour to those 

 whose statements and observations Prof. Lang uses in 

 order to build up his treatise. 



The exact classification adopted by a writer nowadays, 

 in so far as zoology is concerned, is to a large extent a 

 matter of taste. One cannot expect to find oneself in 

 agreement with a colleague on all matters of the kind. 

 Prof. Lang is an authority on the Platodes or flat-worms, 

 and I am glad to see that he assigns them a distinct 

 position as an independent " phylum " of the animal 

 kingdom ; but I think that he has seriously injured the 

 usefulness of his work by recognizing the " Vermes " as a 

 phylum, including in it such diverse groups as the 

 Nemertina, the Nemathelmia, the Annulata, the Proso- 

 pygia, the Rotatoria, and as an appendage (why an 

 appendage when we have already such a mixed lot i") the 

 Chaetognatha. Prof. Lang, after doing this, proceeds to 

 condemn his own action by stating that the so-called 

 phylum of Vermes "is by no means a natural, well- 

 demarcated division of the animal kingdom ; now, as 

 heretofore, it is like a lumber-room, to which all those 

 NO. I 155. VOL. 45] 



groups are relegated which cannot be placed elsewhere." 

 Prof. Lang was not compelled to maintain this ridiculous 

 lumber-room. The consequence of doing so is that he is 

 unable to treat any of the included classes fairly, and 

 that some of the most important problems in morphology 

 are tacitly assumed as solved, or are withheld from the 

 student's consideration. Under the heading " Blood - 

 vascular System," in the chapter on Vermes, we find 

 brought together, and treated as though morphologically 

 identical structures — (i) the canal system of the Nemer- 

 tines ; (2) the sub-cuticular network of the Acantho- 

 cephala ; (3) the sinuses, vessels, and capillaries of the 

 Leeches ; (4) the closed vascular system of Chaetopods ; 

 (5) the tentacular vessels of SipuncuHds ; (6) the red- 

 corpuscled vascular system of Phoronis ; and (7) the 

 unexplored vascular systems of Brachiopods. Neither 

 the method of juxtaposition adopted nor the space given 

 permits the author to discuss whether any two of these 

 so called " blood-vascular systems" are homologous with 

 one another, or whether any one of them is entitled to 

 the name at all. It seems to me that, whilst senior 

 students will be disappointed by the absence of any 

 attempt to deal with the difficult problem of the real 

 nature of the canals and their contained fluids in the 

 cases of Nos, i and 3, the junior student will be seriously 

 misled by the easy assumption that any system of canals in 

 the so-called " Vermes " may be called " a blood-vascular 

 system," and is homologous with any other, and with the 

 standard blood- vascular system, viz. that of man. The 

 entire chapter on the Vermes seems to me to be mis- 

 leading, owing to the author's attempt to deal in a few 

 pages with a number of very different but important 

 groups under this unfortunate heading. 



I need hardly say that I am sorry that Prof. Lang 

 adheres to the old view (p. 540) that " the Arachnoidea 

 are not nearly related to the Xiphosura and fossil 

 Gigantostraca, but are racially connected with the 

 Antennata, and are to be considered as Tracheata which 

 have lost their antennae." It is perhaps only natural that 

 I should distrust the judgment of a zoologist who can at 

 the present day maintain the above propositions. How- 

 ever much I may admire his original work on the 

 Planarians, I cannot consider him a good general guide 

 for the student of zoology. Though I regret Prof. Lang's 

 opinion on this subject, I am not surprised at it, for, in the 

 statement which follows his expression of opinion, he 

 gives a one-sided and erroneous summary of the facts 

 which he thinks can be adduced on either side of the 

 question. Here, as so often elsewhere in the book, one 

 notes the injustice done by Prof. Lang in not citing the 

 name and the work of the author whom he is imperfectly 

 quoting. The student who reads what Prof. Lang has 

 to say on the relationship of the Arachnida to Limulus 

 and the Eurypterines will be misled as to the mere facts 

 of the case, and will not be helped by any reference 

 towards obtaining a fuller knowledge of this interesting 

 matter. 



Though many of the illustrations are excellent. Prof. 

 Lang's book cannot be recommended to English readers 

 either for its originality or for its faithful exposition of 

 cotemporary knowledge. 



The translation appears to be fairly well executed, 

 though the word "apparati," on p. 268, and the repeated 



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