November 28, 1895] 



NATURE 



75 



according to him, a circle round each segment ; by 

 reduction, the more usual number, eight, has been brought 

 about. He refers to Anisochata (which, by-the-by, we find 

 on turning to the systematic part of the w'ork, only a 

 synonym for Megascolex sp.), a perichcCte with only eight 

 bristles on the anterior segments, as a step in this process, 

 which in certain normal octochaetous forms, may go so far 

 as to cause the entire disappearance of bristles from the 

 anterior segments. Since the monograph was in press, 

 Prof. Bourne has published {Quart. Journ. Micr. Sc. xxxvi.) 

 an account of the development of the bristles in the 

 embryo of Peric/iceia, which rather tends to support the 

 view, that the primitive number was eight, and that the 

 perichaetous condition is due to the appearance of 

 additional bristles ; and the fact that a circle of bristles 

 occurs in another family of earthworms, as well as in 

 certain Polychictes, also makes against Beddard's views. 



Another phylogenetic point of special interest is that 

 of the nephridia. Beddard and others have held that 

 the " plectonephric " or " micronephric " condition is ante- 

 cedent to the " meganephric " ; but the ontogeny of three 

 distinct genera contradicts this view, which Beddard, 

 evidently with reluctance, now gives up. I quite agree 

 with him and others, that my group " Plectonephrica " is 

 artificial. 



But while regarding the perichajtous condition as 

 archaic amongst earthworms, he places at the base of 

 the whole Oligochiete tree (p. 173) a genus, Phreoryctes., in 

 which there are usually only^bz^r bristles in each segment. 

 Mr. Beddard recognises the difficulty of his position, but 

 does not meet it in a very convincing manner. The facts 

 of the geographical distribution of the earthworms are of 

 great general importance, for the worms and their cocoons 

 will not withstand prolonged immersion in sea- water, and 

 modes of transference are few ; the cocoons, being buried 

 deep in the earth, are not likely to be carried on the feet of 

 birds. " The characteristic earthworms of New Zealand 

 are Acanthodrilids ; the same family is equally charac- 

 teristic of Patagonia and the adjacent islands ; the only 

 known earthworms from Marion and Kerguelen islands 

 belong to the genus Acanthodrilus. These facts seem to 

 me to be sufficiently important to require the formation 

 of an antarctic region circumpolar in extent " — though it 

 would not necessarily include the Cape. Australia is 

 more closely allied to the oriental region (p. 1 54) than 

 one would have suspected. 



We may heartily congratulate Mr. Beddard on this 

 able and readable monograph which he has found time 

 to write, in addition to publishing many papers on other 

 subjects in connection with his work as Prosector to 

 the Zoological Society; and we may also offer our 

 thanks to the Clarendon Press for undertaking this 

 work. The book consists of 725 quarto pages of text, 

 together with 85 pages of bibliography, and a full index 

 (from which, however, we miss Anteus) ; there are five 

 lithographed plates, and numerous illustrations in the 

 text ; it is well printed, with wide margins, and simply 

 but effectively bound. But, while offering our congratu- 

 lations, we must also record a grumble ; for there are one 

 or two omissions which detract from the usefulness of 

 the work, from a systematist's point of view. (1) A tabular 

 statement of the classification adopted, would have 

 NO. I 36 I, VOL. 53] 



rendered his views more clearly and more readily than 

 having to weed it out of the text ; (2) a synopsis of 

 differential family characters in tabular form, such as we 

 find in the recent Catalogues of the British Museum, 

 would enable one to refer an earthworm to its family with 

 comparative ease. Tables of generic characters there 

 frequently are ; but they are often so ill-arranged as to 

 be of comparatively little use. Some of these tables 

 extend across two entire pages of fifty lines or more, and 

 it is extremely difficult for the eye to follow these lines 

 across the wide margins of the two pages (pp. 532-533), 

 especially when, as in p. 632 of my copy, the pages are 

 so bound that the lines do not correspond. This matter 

 might have been so easily remedied by numbering the 

 lines on each page. 



Lists of the genera recognised as good, are usually 

 given after the discussion of the family characters ; but 

 in some cases, as in Perichaetida^, the list does not 

 appear. 



The number of plates seems very inadequate to the 

 text, and it is not evident what plan has been followed 

 in selecting the species figured to illustrate the vascular 

 system, for example ; for not one of the figures pretends 

 to give a complete plan of the system, and the chief 

 types even are not represented. Plate v. will remain a 

 mystery to many readers. The diagrams of the repro- 

 ductive organs, which are on the plan adopted by me in 

 my " Attempt to Classify Earthworms," might have 

 been, with advantage, increased in number so as to 

 include every family. 



Such interesting matters as the encysted .-Eolosoni, 

 and the peculiarly modified genital setie of Acantho- 

 drilids, might well have been illustrated. 



In such an extensive work as this, misprints and smaller 

 errors can scarcely be excluded, but they are very rare ; 

 nevertheless, we think that all measurements should 

 have been given in the metrical system. Here and there 

 one finds "inches" cropping up {Geoscolex maximits); 

 and sometimes, where the original measurements were in 

 inches, the transformation to millimetres has been worked 

 out wrongly {Plagiochceia). 



But with all its faults, the monograph redounds to the 

 credit both of the author and the publishers, and is a 

 most welcome addition to our zoological standard works. 



W. B. Benh.^m. 



DYNAMICS. 

 Dynamics. By P. G. Tait, M.A., Sec. R.S.E. Pp. 361. 

 (London : Adam and Charles Black, 1895.) 



THE main substance of Prof. Tait's present work has, 

 for the past twelve years, been accessible to any one 

 who cared to be at the trouble of consulting the cumbrous 

 volumes of the " Encyclopaedia Britannica," but we are 

 glad that the author has at last been induced to issue his 

 article on " Mechanics" in the form of a compact and handy 

 octavo volume. This will be a useful addition to the 

 library of every teacher who has to lecture to advanced 

 classes, but the very encyclopaedic treatment of the 

 subject makes it rather hard to judge how far Prof. Tait's 

 work meets the requirements of students. The author 



