48 REPORT ON THE TUNICATA OF PLYMOUTH. 



naturalists, by Forbes and Goodsir, by Alder and Hancock, and by 

 Professor Huxley ; but various causes have liitberto conspired to 

 delay its production. It is now very satisfactory to be assured 

 that the preparation of the Monograph is in the hands of the 

 experienced author of the Eeports on the " Challenger" Tunicata. 

 In the meantime a more or less detailed account of the forms 

 with which I have met at Plymouth may be of some service as a 

 contribution towards an improved knowledge of the British repre- 

 sentatives of the group. 



In the neighbourhood of Plymouth I found the rocks under the 

 Hoe, the north and east sides of Drake's Island, the wooden piles of 

 the docks and wharves in Millbay and the Catte water, the rocks and 

 tidal pools of the Mewstone and Wembury Bay, to be all good 

 hunting-grounds for the littoral species of composite Tunicata ; the 

 best dredging-grounds for Ascidians generally were undoubtedly 

 the neighbourhood of the Duke Eock, the Queen's Grounds, and 

 the deeper waters off the Eddystone, the Mewstone, and Bigbury 

 Bay, while some forms were most common upon Zostera in Cawsand 

 Bay ; but it was almost impossible to use any of the ordinary 

 methods of collecting within Plymouth Sound without obtaining 

 numbers of Ascidians of various species. Very few simple Ascidians 

 were to be found inhabiting the tidal zone ; they were most plentiful 

 in the deep water of the trawling grounds and on the rough ground 

 off the Mewstone. 



In reporting upon the Ascidians of Plymouth, I have taken 

 Clavelina and its allies as my starting-point, since this genus includes 

 the forms which are in many respects probably the least modified 

 descendants of the earliest Ascidiacea. But I am met at the outset 

 by the problem which is now engaging the attention of every 

 Ascidiologist : What taxonomical value must be attributed to the 

 possession of the power of budding and of the formation of colonies ? 

 A full discussion of this question I cannot give here, but since the 

 matter bears directly upon the classification which I shall employ, I 

 am bound to admit that the division of the Ascidiacea into the sub- 

 orders Ascidise simpUces, Ascidiai composita^, and Ascidise salpiformes 

 so completely disregards the admitted inter-relationship between 

 various sections of these groups, that its adoption seems to me to 

 involve the rejection of any morphological, and therefore genetic, 

 meaning in classification altogether. The term '' composite Asci- 

 dians " is in practice a very convenient one, but this is not a 

 sufficient reason for retaining it as the symbol of a natural group, 

 when the group in question is in reality no natural group at all, but 

 an '' artificial assemblage " composed of several quite unrelated 

 phyla. The primary subdivision of the Ascidiacea into these three 



