546 



NA TURE 



[October 4. 1900 



The direct and positive evidence which is available 

 may seem at first sight an insufficient foundation for the 

 hypothesis of a Pelmatozoic ancestor of all Echinoderms, 

 that is to say, a pre-Cambrian form in which the food- 

 grooves initiated a radiate symmetry with which all 

 other systems of organs gradually fell into line. But the 

 necessity of some such assumption becomes irresistible 

 when we realise by careful reflection the inadequacy of 

 any other theory to account for the evolution of the 

 characteristic radiate symmetry and the complete hold 

 it has taken upon all organs of the echinoderm body. In 

 the ontogeny of existing types it always seemsas if it were 

 the hydrocoele or water vascular system which actually 

 set the tune to which all the other systems of organs 

 dance, but it is difficult, if not impossible, to imagine 

 clearly a course of ancestral evolution, limited and 

 guided, as it must have been, by the necessities of the 

 struggle for existence, in which the hydrocoele took the 

 initiative in this respect, and did not itself follow the 

 lead of some other system. The hydrocoele of the 

 Pelmatozoic ancestor was probably at its first origin 

 simply a compartment of the coelom which had the 

 function of furnishing tactile tentacles, formed as hollow 

 outgrowths of the body-wall, in connection with the food- 

 grooves. On this hypothesis it is easy to understand 

 why the hydrocoele was the first system of organs to 

 be affected by the radiate symmetry initiated by the 

 primitive nutritive system, and consequently why, in the 

 Eleutherozoa, after atrophy of the food-grooves, the 

 symmetry should apparently start from the hydrocoele 

 itself. 



In the present volume the Pelmatozoa are also under- 

 taken by Mr. Bather, who recognises four classes — 

 Cystids, Blastoids, Crinoids and Edrioasterids. Another 

 and perhaps more natural {i.e. phylogenetic) classification 

 is hinted at (p. 39), but the arrangement quoted above is 

 adopted as involving the least disturbance of established 

 names and ideas. The Pelmatozoa occupy about two- 

 thirds of the volume, and the treatment of this most 

 difficult group cannot be too highly praised. An expert 

 in this branch of zoology might perhaps find details to 

 criticise or ideas with which to disagree ; the worker in 

 other fields can only express his appreciation of the eru- 

 dition displayed and the labour expended in setting forth 

 the structure and evolution of this vast series of forms. In 

 a group which is to a large extent represented by fossils, 

 and in which so little material is available at the present 

 day for the scalpel and the microtome, it is natural that less 

 space and attention should be given to the anatomy and 

 morphology of the soft tissues than to that of the 

 skeleton and its never-ending complications of plates 

 and ossicles. A simple Crinoid is taken as a type of 

 Pelmatozoic organisation, and its anatomy is briefly de- 

 scribed. One small point, at least, in this description is 

 open to criticism. The author.identifies Ludwig's blood- 

 vessel and ring in the Crinoid as the " pseudhaemal," i.e. 

 perihaemal, system (pp. 100 and 102). This seems to 

 be an oversight, as elsewhere (p. 26) he states that 

 this system " is so much reduced in Crinoidea 

 that its existence is denied by some authors." 

 Since the perihaemal system of canals, where well 

 developed, as in the starfish, has been shown very 

 clearly to be of coelomic origin, it is impossible to identify 

 NO. 1614, VOL. 62] 



with it the Crinoid "blood-vessel," which has all the 

 characters of the canals termed in this work the 

 "lacunar" or"ha;n>ar' system. If anything in the 

 Crinoid arm is to be identified as perih.emal (a term 

 we much prefer to pseudhremal), then probably the sub- 

 tentacular canals have the most right to this title, as 

 being coelomic canals which occupy approximately the 

 same position as the perihaemal canals in the starfish, 

 and which have also the same relation to the lateral 

 nerve cords that the perihaemal canals have to " Lange's 

 nerves." On this view we should have to regard the 

 perihaemal system as a portion of the coelom, which in 

 the Pelmatozoa has reached only an incipient degree of 

 specialisation, being in the region of the disc completely 

 merged in the general body-cavity. 



The account of the Holothurians has been written by 

 Mr. E. S. Goodrich, who gives a useful summary of our 

 present knowledge of the group. The remaining 

 Eleutherozoa — Stelleroidea and Echinoidea — have been 

 undertaken by Prof. J. W. Gregory, whose researches on 

 these groups are well known to zoologists, and who gives 

 us a most valuable and complete account of them. It is 

 necessary, however, to point out a few errors or over- 

 sights which have crept in, some of which are important, 

 though they do not detract from the value of the work 

 as a whole. On p. 261 it is pointed out that we are 

 indebted to Sladen for a memoir on the aberrant form 

 Astrophiura., and the work is quoted in due course 

 amongst the literature of Stelleroidea, but nowhere else 

 is any reference made to Astrophiiira and its peculiari- 

 ties ; it is omitted from the classification, does not appear 

 in the index, and is, in fact, ignored altogether. The 

 genus Ophioteresis is used as an argument for 

 uniting the Asteroids and Ophiuroids on the ground 

 that " the radial ambulacral vessels and nerve 

 trunks lie in shallow grooves on the ventral surface 

 of the anus " (p. 262 ; also pp. 270 and 274). The 

 author gives no definite authority for this statement, but 

 leaves us to infer that he obtains the fact from Bell's 

 description of the genus. Bell, however, did not describe 

 any such condition as that which Gregory dwells upon 

 so often and makes the basis for such important de- 

 ductions, and it is highly improbable that it occurs at all. 

 It is much more probable the ambulacral vessels and 

 nerve trunks pass in Ophioteresis through the aperture 

 in the centre of the vertebral ossicle which Gregory 

 figures plainly enough (Fig. xiv.), while maintaining a 

 discreet silence about it. Finally, it must be mentioned 

 that the peristomial plates in the Ophiuroid mouth 

 skeleton are not " between the mouth frames and the 

 buccal shields " (p. 264), but are above, i.e. to the aboral 

 side of, the former, according, at least, to the careful 

 descriptions and figures of Ludwig ; the "mouth fi-ames" 

 are between the buccal shields and the peristomial plates. 



A conscientious reviewer does his best to find mistakes 

 in the works submitted to his scrutiny and judgment. 

 In the present instance it cannot be said that we have 

 been very successful in our search, having regard to the 

 size and scope of the work. In conclusion, we can but con- 

 gratulate heartily the editor, authors and publishers on 

 the very valuable treatise they have produced, a work 

 which reflects credit on all concerned, and is a triumph 

 for English zoology. E. A. M. 



