NATURE 



545 



THURSDAY, OCTOBER 4, 1900. 



A MANUAL OF THE ECHINODERMS. 

 A Treatise on Zoology. Edited by E. Ray Lankester, 

 F.R.S. Part iii. The Echinoderma. By F. A. Bather, 

 J. W. Gregory and E. S. Goodrich. Pp. ix + 344. 

 (London : A. and C. Black, 1900.) 



THE first instalment of the long-expected "Oxford 

 Zoology " — first, that is to say, in order of publica- 

 tion — will be heartily welcomed as filling a distinct gap 

 in zoological literature, and not of this country alone. 

 During the latter half of the nineteenth century scientific 

 literature has accumulated with such rapidity as to 

 render it practically impossible for a zoologist at the 

 present day to master thoroughly more than a limited 

 part of his subject. To acquire a knowledge of the 

 results gained in fields other than that which he has 

 made his speciality, he must be dependent to a large ex- 

 tent upon the manuals and guide-books compiled by those 

 who are sufficiently familiar with the latest discoveries 

 in particular branches of zoology to be able to give a 

 clear and critical account of the present state of know- 

 ledge in these departments. Nowhere is this necessity more 

 strongly felt than in dealing with the Echinoderms,a group 

 in which the student is confronted, on the one hand, with 

 intricate morphological problems and with phylogenetic 

 questions of a most puzzling kind ; and, on the other 

 hand, with such a vast array of extinct types that the non- 

 expert feels at once out of his depth when attempting to 

 obtain an adequate knowledge of them. In the Pelma- 

 tozoa, practically half the phylum, we find a group of the 

 greatest historical and phylogenetic importance, but one 

 in which the existing forms teach us no more about the 

 race in the past, and regarded as a whole, than do the 

 modern Egyptians about the former dynasties whose 

 remains are entombed in their land. The abundance of 

 forms unearthed by the palzeontologist has called forth a 

 literature which exemplifies fully the danger of some- 

 thing like a deadlock in zoological science, as the result 

 simply of its fertility. The student soon loses his way 

 and finds himself struggling with a mass of hard facts 

 and contradictory hypotheses, due on the one hand 

 to the great diversity of form and structure in the objects 

 themselves, and on the other hand to difficulties insepar- 

 able from the study of animals known almost entirely as 

 fossils. Any one who has endeavoured, for instance, to 

 gain an acquaintance with the structure and evolution of 

 fossil Crmoids from the voluminous works of Messrs. 

 Wachsmuth and Springer and other writers must have 

 felt the urgent need for a guide and interpreter, failing 

 whom It was necessary either to study deeply or to 

 pass lightly by, to become an expert or to be 

 content with ignorance. Yet no one with even a 

 superficial acquaintance with the problems of Echinoderm 

 morphology and phylogeny would willingly pass over 

 the extinct forms, and least of all the more ancient 

 Pelmatozoa, such as the Cystids and their allies, since it 

 is obvious that here, if anywhere, is to be found in a 

 concrete form the solution of many puzzles in the evo- 

 lution of the phylum. Nowhere is palaeontology, as a 

 source of material evidence for theories of phylogeny, 

 given so fair a trial as in the case of Echinoderms with 

 NO. 1614. VOL. 62] 



their complete skeleton and consequent abundance of 

 well-preserved fossil types, and it must be conceded that 

 palaeontology, if it condescends to speak clearly, can 

 give the only final judgment in questions of evolution 

 and ancestral history. 



For many reasons, therefore, a plain and intelligible 

 account of the Echinoderms, and especially of the 

 Pelmatozoa, by those who have an expert knowledge of 

 them, both as fossils and as recent forms, was greatly to 

 be desired, and in the present volume we have the first 

 complete treatise that has been published under these 

 conditions in any language. The intention of the authors 

 is to give a systematic account of the Echinoderms, 

 including every known genus, living or extinct, and at 

 the same time to trace as far as possible the evolution 

 and relationships of the forms comprised under each 

 class or order, as inferred both from their structural 

 affinities and from their succession in time. The aim in 

 view is therefore to effect a happy combination of the 

 older styles of systematic treatise with the modern 

 methods of comparative morphology, developmental 

 history and phylogenetic speculation. 



An introductory chapter, giving a general description 

 of the organisation and development of Echinoderms, 

 from the pen of Mr. Bather, attempts to trace the origin 

 of the characteristic radiate symmetry from the bilateral 

 ancestor represented by the Dipleurula larva. Like 

 most other recent authorities on the group, Mr. Bather 

 supports the opinion that the radiate symmetry was ac- 

 quired in all Echinoderms during an ancestral fixed 

 stage, in which the animal fed by means of currents 

 produced by cilia and directed along special food-grooves 

 towards the mouth. In all animals with this mode of 

 nutrition, which was probably the primitive method in 

 each of the principal phyla, except perhaps the Cnidaria 

 and the Arthropods, the general tendency of evolution 

 is towards a reduction or loss of active locomotion, and 

 frequently towards fixation, which certainly occurred in 

 the Echinoderms. The common ancestor of the phylum 

 was, in fact, to all intents and purposes, a Pelmatozoon, 

 fixed by the aboral pole, the original right side of the 

 bilateral ancestor, and with ciliated grooves converging 

 to the mouth on the upper side. Amongst the Cystids 

 ancestral stages are to be found showing the gradual 

 acquisition of a radiate pentamerous symmetry, first by 

 the food-grooves and then by the skeleton and other 

 organs of the body, last of all by the gonads. The 

 Pelmatozoa retained permanently this mode of life, con- 

 tinually adapting and perfecting their organisation to 

 the necessities entailed by it. The other Echinoderm 

 classes, on the other hand, grouped together as 

 Eleutherozoa, and including the modern starfishes, 

 sea-urchins and holothurians must have become free 

 again at a very early period after the acquisition of 

 radiate symmetry, giving up their method of nutrition 

 by means of ciliary currents, and losing in consequence 

 their food-grooves, which atrophy as such, the condensa- 

 tion of the nerve-plexus at the base of the grooves per- 

 sisting, and being further specialised as the "superficial'' 

 nervous system. The holothurians were the first stock to 

 become Eleutherozoic, radiate symmetry in their case 

 not having extended to the gonads, as it has in the case 

 of the starfish and urchins. 



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