50 



NATURE 



[May 2 1, 1908 



methods of the dissecting- room ; it must be read as a 

 whole to be appreciated. Its perusal will be found 

 to give both pleasure and a real acquisition in know- 

 ledge. Mr. Rogers is to be congratulated on the 

 production of a volume in every way worthy of its 

 place in a series designed by one so conversant with 

 our colonial empire as Sir Charles Lucas. 



John \. Cockburn. 



BRITISH ASCIDIANS. 

 The British Tunicata. .An unfinished Monograph by 

 the late Joshua .Alder and the late .Albany Hancock. 

 Edited by John Hopkinson. Vol. ii., with Lives of 

 the Authors by Canon .A. M. Norman, F.R.S., and 

 the late Dr. Dennis Embleton. (London : Ray 

 Society, 1907.) Price 25^. net. 



THE first volume of this work was published in 

 1905, and was noticed in N.ature in the follow- 

 ing year (vol. Ixxiii., p. 508). So far as the so-called 

 " simple " and " social " .Ascidians are concerned, the 

 work is now complete. No statement is made as to 

 whether we are to expect a third volume on the 

 " compound " Ascidians. We understand, however, 

 that such a volume is in preparation, and that it will 

 include a bibliography of the Tunicata by the editor. 

 We may repeat our congratulations to the Ray 

 Society for publishing this long-lost work, and to 

 Mr. Hopkinson for his careful editorship under 

 many difficulties. The numerous coloured and photo- 

 graphic plates included in this volume maintain the 

 same high standard as in its predecessor, and the 

 lives of the authors, by their friends Canon Norman 

 and the late Dr. Embleton, which are prefi.xed to this 

 volume, are full of interest for all who can appreciate 

 the simplicity of nature and patient genius of two of 

 the most distinguished pioneers in the field of British 

 marine zoology. 



Mr. Hopkinson has, with one exception, limited his 

 notes to the addition of bibliographic and distribu- 

 tional records published before 1871. The monograph 

 consequently possesses as nearly as possible the char- 

 acter which it would have assumed if it had been 

 published in the latter year, two years before Han- 

 cock's death. 



The present volume deals with Ciona and Corella 

 among the Ascidiadas, and with the families Mol- 

 gulidae, Cynthiadce, and Clavelinidae, in the broadest 

 sense of these various terms. Between fifty and sixty 

 " species " are described, of which no less than eleven 

 are put forward as new. Three of the latter are re- 

 ferred to the genera Molgula, Cynthia and Clavelina 

 respectively, two to Styelopsis, and six to Styela. In 

 most of these cases it is more than doubtful whether 

 the characters relied upon by the authors possess sufli- 

 cient stability to serve as a criterion of specific 

 differences. Some of these " new species " are un- 

 doubtedly mere variants from common types, together 

 with other forms which are described in the mono- 

 graph under names previously conferred upon them 

 by the authors and other naturalists. The " new " 

 species Clavelina corrugata is described as differing 

 from the common C. lepadifonnis merely in the 

 NO. 2012, VOL. 78] 



wrinkling of the test and in the pinkish colour of the 

 pharyngeal stripes, which are white or yellowish in 

 the common type. A single tide-pool on the Devon- 

 shire coast will occasionally show half a dozen equallv 

 well-marked variants from the same type. 



It would be tedious, as well as unprofitable, in this 

 notice to enter upon a detailed comparison of the 

 authors' nomenclature of recognised species with the 

 systems in current use. But it is to be hoped that the 

 publication ot this monograph will not have the result 

 of introducing farther confusion into a subject already 

 sufficiently tangled, in which the more critical re- 

 vision work of the last twenty years has not yet pro- 

 duced complete concordance of results. The revival 

 of Miiller's conchilega for a species of Molgula is 

 particularly unfortunate, for there is good reason to 

 regard M tiller's type as a common species of .Ascidin, 

 while .\lder and Hancock's Molgula conchilega is 

 plainly identical with Kupffer's Molgula occulta. It 

 is doubtful, by the way, if Mr. Hopkinson is justified 

 in assigning to this species the various records of 

 Ascidia conchilega which have been based upon 

 MClUer's original description. The substance of a 

 remark which I made in my previous notice may be 

 fitly reiJeatcd, that the monograph, after all these 

 years, must be cautiously used as a repository of 

 descriptions and figures, but not as a guide to the 

 classification or nomenclature of the group. 



In one respect Mr. Hopkinson has departed advan- 

 tageously from his rule not to add any observation of 

 later date than 1870, since he has incorporated a 

 definition of the genus Styelopsis, which was founded 

 in 1S82 by Traustedt for the common Styela grossu- 

 laria, a species which Alder and Hancock themselves 

 rt cognised as markedly distinct from the other species 

 of .Stvela. In these circumstances the editor 

 might well have pointed out that the form described 

 by Victor Carus as Thylaciuin sylvani, which is in- 

 cluded in this monograph under that name, is in all 

 probability nothing but Styelopsis grossularia, of 

 which the young individuals, fixed on the tests of the 

 parents, had been erroneously regarded as evidence 

 of gemmation. I can confirm all that Michaelsen has 

 recently said on this point (" Revision der composi- 

 ten Styeliden oder Polyzoinen," Hamburg. 1904), 

 with some additions, since in 1891, with the permis- 

 sion of the Linacre professor, I dissected a portion of 

 Carus's type in the Oxford Museum, and found it to 

 be identical in structure with S. grossnlaria, while 

 the so-called buds were true metamorphosed larvae, 

 possessing characteristic protostigmata (Proc. Royal 

 Soc, li., pp. 505-13). In the following- year also 1 

 searched the original locality, and many others, in the 

 Scilly Islands, and found the same species covering 

 th2 rocks in immense numbers, as described by Carus 

 in the case of Thylaciuin sylvani. It is interesting to 

 notice that in this monograph .Alder and Hancock 

 record the fact that they also had " seen " the original 

 specimen in the Oxford Museum, and record their 

 doubts as to the existence of gemmation, as well as 

 their impression of the " very close resemblance 

 between the Thylacium sylvani and some of the 

 smaller gregarious Cynthiae already described." The 



