NATURE 



THURSDAY, MAY 27 



1909. 



T^ 



TWO STANDARD WORKS O.V ZOOLOGY. 



(i) A Student's Text-book of Zoology. By Prof. Adam 

 Sedgwick, F.R.S. Vol. iii. The Introduction to 

 Arthropoda, the Crustacea, and Xiphosura. By J. J. 

 Lister, F.R.S. The Insecta and Arachnida. By Dr. 

 A. E. Shipley, F.R.S. Pp. xii + 906. (London : 

 Swan Sonnenschein and Co., Ltd., 1909.) Price 24^. 

 (2) .1 Treatise on Zoology. Edited by Sir Ray 

 Lankester, K.C.B., F.R.S. Part vii. Appendicu- 

 lata. Third Fascicle, Crustacea. By Dr. W. T. 

 Caiman. Pp. viii + 346. (London: A. and C. 

 Black, 1909.) Price 155. net. 



""HESE two ample volumes suggest that a compre- 

 -L hensive text-book on the whole animal kingdom 

 can no more be written by a single zoologist. The 

 advanced student needs an encyclopaedic work in 

 which several naturalists whh wide general and deep 

 special knowledge have united their labours. The 

 great " Treatise " which is slowly taking shape under 

 the editorship of Sir Ray Lankester has been planned 

 from the outset on these lines, and Dr. Caiman's 

 volume is worthy of the best of its predecessors. Prof. 

 Sedgwick now issues the third volume of his text- 

 book, eleven years after the appearance of the first, 

 and he tells us in his preface that, but for the help of 

 his colleagues, Messrs. Lister and Shipley, this present 

 volume would still be far from completion. 



(i) When Prof. Sedgwick's second volume was re- 

 viewed in Nature (November, 1905), the arrangement 

 by which the Chordata were placed in the middle of 

 the series, and the Arthropoda widely separated from 

 the Annelida, was naturally criticised. The author, in 

 his preface, now briefly replies to this criticism, point- 

 ing out that he followed " the clue given by the 

 coelom," and postponed the section on the Arthropoda 

 until after that on the " enterocoelic " phyla. In de- 

 fending this separation of the Arthropoda from the 

 Annelida Prof. Sedgwick differs from Sir Ray Lan- 

 kester, who adopts a single phylum — the " Appendi- 

 culata " — to include Arthropoda, Annelida, and Roti- 

 fera. Prof. .Sedgwick is fully justified in regarding 

 the Arthropoda as an independent phylum, as thev 

 " differ so fundamentally from the Annelida in their 

 coelomic arrangements," but in separating the two 

 groups so widely in his system he surely puts too 

 great a strain on the fascinating coelomic theory. 



To the volume before us Prof. Sedgwick himself 

 contributes the chapters on the Tunicata, Entero- 

 pneusta, Echinodermata, Onychophora, an.d Myria- 

 poda. His account of the Tunicata, which occupies 

 sixty-five pages, is a masterly summary of the complex 

 details of structure and life-history which characterise 

 that interesting and puzzling class. The author's 

 scepticism as to many current morphological ideas is 

 shown by his remark that the ascidian subneural 

 gland is " in its origin actually a part of the embryonic 

 brain which the pituitary body never is." Nearlv 

 fifty pages are devoted to the Enteropneusta, a testi- 

 mony to the great advances lately made in our know- 

 ledge of the group and to its zoological importance. 

 XO. 2065. VOL. 80] 



While upholding the vertebrate affinities of the 

 Enteropneusta, Prof. Sedgwick insists that several 

 fundamental features clearly indicate relationship to 

 the Echinodermata, and his account of that great 

 phylum, occupying nearly 200 pages, comes next in 

 the volume. His discussion on the relationship 

 between echinoderms and chordates is especially 

 valuable and suggestive. Besides the well-known cor- 

 respondences in the coelomic spaces, the central nervous 

 system, and the mesodermal limy skeleton, and the 

 likeness of the tornaria to the echinoderm type of 

 larva, attention is directed to the left-hand position 

 of the mouth, both in the developing echinoderm and 

 in the larval Amphioxus. This character is considered 

 of the greater importance because no adaptational ex- 

 planation of it, at least in the latter instance, is forth- 

 coming. Incidentally, the author discusses the 

 Dipleurula theory as elaborated by Bather, and gives 

 reasons for doubting the existence of bilateral sym- 

 metry among the ancestors of echinoderms, though 

 he has no other explanation of the free-swimming 

 larvae to offer. He further differs from most special, 

 students of the Echinodermata in his rejection of the- 

 association of the Crinoidea with the Palaeozoic Blas- 

 toidea and Cystidea in a sub-phylum Pelmatozoa, hold- 

 ing our knowledge of the structure of the two latter 

 classes to be too incomplete for any certain estimation 

 of their affinities, while " Holothurians stand further 

 from Asteroids and Echinoids than do the Crinoids." 

 The value of the chapter on echinoderms is much 

 enhanced by a remarkably well-chosen series of illus- 

 trations, including some hitherto unpublished drawings 

 by Prof. E. W. MacBride. 



The remainder of the volume (about 550 pages) is 

 devoted to the Arthropoda. Mr. J. J. Lister con- 

 tributes a short but admirable introduction on the 

 phylum as a whole. On the disputed question of 

 the segmentation of the crustacean and insectan head, 

 Mr. Lister follows in the main the views of Hansen 

 and Folsom, accepting the maxillulae of the Apterygota 

 as true appendages; but he ranges the arachnidan 

 chelicerce with the insectan feelers, and thus makes 

 the whole cephalothorax of a scorpion equivalent to 

 the head of a cockroach. There is a remarkably good 

 account of arthropodan eyes and vision. 



(2) Mr. Lister has also written the chapter on the 

 Crustacea, which occupies some 200 pages, and this 

 section can be appropriately compared with Dr. 

 Caiman's volume of Lankester's "Treatise." In the. 

 former work the Trilobita are included among the 

 Crustacea, while in the latter they are relegated to 

 the Arachnida. Both writers agree that this ancient 

 group of arthropods has affinities with the Arachnida ; 

 and with the typical Crustacea, but, in view of their 

 feelers and biramous limbs, their actual inclusion 

 among the Arachnida can hardlv be defended. In 

 the classification of the Crustacea Mr. Lister is con- 

 servative, preserving the Entomostraca as a subclass, 

 and holding to the long-recognised and familiar orders. 

 Dr. Caiman, on the other hand, rejects the Entomo-. 

 straca as a natural group, and raises the Copepoda, 

 Ostracoda, Cirripedia, &-c., to the rank of " subr 

 classes," dividing each into two or more " orders." 



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