March 29, 1906] 



NA TURE 



509 



For these reasons the student of the Tunicata cannot 

 be otherwise than grateful to the Ray Society for the 

 publication of this work, and especially for the 

 liberality with which it has been illustrated. The 

 coloured figures representing many of the authors' 

 species must rank among the best figures of ascidians 

 extant, and the numerous collotype reproductions of 

 Hancock's drawings of the branchial sac, &c, will 

 greatlv facilitate the task of identification. 



The first volume, which we hope may soon be 

 followed by the remainder of the work, contains 



(1) the authors' introduction (a historical summary of 

 British records of Tunicata up to the year 1S70), (2) a 

 reprint of Hancock's paper " On the Anatomy and 

 Physiology of the Tunicata " (published by the 

 Linnean Society in 1S67), and (3) an account of thirty 

 British species referred by the authors to the genus 

 Ascidia. Two of these so-called species are now- 

 described for the first time, viz. Ascidia amoena and 

 Ascidia Morei. 



It is no discredit to the memory of the distinguished 

 authors of this monograph, whose general accuracy 

 of observation has long been established, if we express 

 a conviction that no modern expert in this group of 

 marine animals will be prepared to recognise the 

 claims of half Alder and Hancock's " species " to 

 specific rank. It is not improbable that the thirty 

 forms described in the monograph will be ultimately 

 referred to some ten or twelve " good species " at 

 most. 



Excluding Ascidia canina, the relations of which to 

 Ciona intestinalis, L., appear, strangely enough, to 

 have been overlooked by Hancock, the remaining 

 twenty-nine species of Ascidia, as described by the 

 authors, would in these days be referred to the three 

 genera Phallusia (with the single species mamillata), 

 Ascidia and Ascidiella of Roule. Adopting for the 

 moment Alder and Hancock's specific names, and con- 

 fining our attention to the forms dealt with in their 

 monograph, we may say that each of the genera Ascidia 

 and Ascidiella includes three main types. To Ascidia 

 (s. sir.) belong (1) mentula, with which robusta, rttbi- 

 cunda. and rubrotincta are probably synonymous; 



(2) mollis, with crassa, plana, Alderi, and possibly 

 ritdis, as allies; and (3) plcbeia (= conchilega of 

 Muller), with which producta, inornata, and depressa 

 are closely related or synonymous. To Ascidiella 

 belong (1) obliqua ( = prunum of Muller), to which the 

 new species amoena appears to be related; (2) venosa, 

 and (3) a large series of very variable forms referable 

 in the main to the types sordida ( = virginea of 

 Muller), scabra, and pustulosa ( = aspersa of Muller), 

 of one or other of which the authors' " species " 

 elongata, aculeata, Morei, Normani, affinis, elliptica, 

 pellucida, orbicularis, and vitrea appear to be merely 

 varieties or local forms. 1 



There is probably no group of animals in which 

 external conditions exert a greater influence upon 

 the size, shape, and structure of the body than in 

 the case of the ascidians, owing to their permanent 



1 For a fuller discussion of the relations of particular species special 

 reference should be made to Prof. Herdman's paper in Jour. Linn. Sec, 

 xxiv., 1893, and Hartmeyer's " Holosome Ascidien " in " Meeresfauna von 

 Bergen," 1901. 



NO. I9OO, VOL. 73] 



fixation under the most diverse natural conditions, 

 their mode of feeding, and the plastic character of 

 the test which serves them for a skeleton. Differences 

 in the supply of food alone — and no factor is liable 

 to greater extremes than the amount of phytoplankton 

 in littoral waters — must influence the development of 

 an ascidian's body in so many different ways that 

 great variability must be the rule rather than the 

 exception. In these circumstances it is doubtful 

 if the natural history of this group can be adequately 

 treated in any monograph until much additional work 

 has been done, not only in the systematic observation 

 of the nature and extent of local variations, but also 

 in direct experiments concerning the effect of different 

 conditions upon the growth of the progeny of selected 

 parents. Until such work has been done, any attempt 

 to define specific limits within (e.g.) the virginea- 

 scabra-aspersa group must remain a mere expression 

 of personal opinion. 



In the meantime the publication of the present work 

 is likely to lead to the clearing up of many uncer- 

 tainties, provided it is regarded mainly as a repository 

 of facts, and not as an authoritative guide to the 

 classification or nomenclature of the group. 



This aspect of the work has been fortunately 

 retained under the editorship of Mr. Hopkinson,. 

 who has restricted his notes to the addition oi 

 such bibliographic and distributional records, pub- 

 lished prior to 1871, as were necessary for the com- 

 pletion of the authors' MSS. up to the date of 

 Hancock's latest work. The editorial footnote " on 

 the intimate relationship existing between the Tuni- 

 cata and the Polyzoa," on the first page of the 

 authors' introduction, conveys just the right touch of 

 archaic suggestiveness. 



We notice a couple of misprints : Weigmann for 

 Wiegmann (pp. 7 and 12), and Mongula for Molgula 

 (p. 46) ; and may point out that Figs. 8 and 9 on 

 plate xi. represent not " probably a variety of Corella 

 parallelo gramma," but Hancock's own species, Corella 

 larvaeformis, which we presume will be described in 

 the second volume of the monograph. 



W. Garstang. 



THE METALLURGY OF IRON AND STEEL. 

 Elementary Practical Metallurgy, Iron and Steel. By 

 Percy Longmuir. Pp. xiii + 270-l- 13 plates. (Lon- 

 don : Longmans, Green and Co.) Price 55. net. 

 "\ "WORKS on practical metallurgy have generally 



VV consisted of descriptions of series of experi- 

 ments suitable for performance in an ordinary labor- 

 atorj possessing the usual equipment with small assay 

 furnaces; but this book is an elementary work on the 

 metallurgy of iron and steel, written with the view 

 not only of serving the needs of the ordinary beginner 

 among students, but of attracting the severely prac- 

 tical man to the study of metallurgical literature, and 

 thus helping him ultimately to the position of being 

 able to throw the light of new discoveries on his daily 

 work, and to make application of suitable results— 

 evidently a practical apostle of the methods of the 

 British Science Guild. The writer thoroughly agrees. 



