560 PEOF. w. A. heedman's eevised 



cannot express adequately the relations existing between tlie 

 various groups, still I believe that these groups are all natural 

 assemblages, with the exception of the " Ascidige Compositse," 

 which is to be regarded as being polyp hyletic in origin, having 

 been derived from several distinct groups of simple Ascidians 

 which have independently acquired the j^roperty of budding so as 

 to form colonies. I beHeve, then, that although it is a matter of 

 convenience to retain still the suborder Ascidise Compositse, it 

 may some day become necessary to break up this artificial assem- 

 blage of colonial forms, and to place the sections beside their 

 nearest allies amongst the Ascidise Simplices. 



I have purposely abstained from being too critical in regard 

 to closely related or poorly defined genera and species, believing 

 it to be more useful in this preliminary revision of the group ro 

 admit all such doubtful forms if they have any characteristic by 

 which they can be distinguished. A number of the older species 

 of the Tunicata require to be examined afresh (those it is possible 

 to obtain) and re-described, as the original descriptions are no 

 longer sufficient to characterize them properly and to distinguish 

 them from the numerous species which have been described (more 

 fully) since. I have thought it better to err on the side of ad- 

 mitting iuto the tables some of these imperfectly characterized 

 species rather than to run the risk of doing an injustice to former 

 authors by suppressing species which may eventually turn out to 

 be distinct and entitled to recognition. Others of the older species 

 which in the present state of our knowledge cannot be placed in 

 the tables, but which I do not know to be mere synonyms, have 

 been referred to in footnotes or put in separate lists under the 

 genera to which they probably belong. 



I have inserted the authorities and the dates of formation of 

 the various groups, but have not considered it necessary to 

 encumber the text with references to the original papers. There 

 can be no difficulty from the author's name and the date ia 

 finding the work in question in any bibliography of the Tuni- 

 cata, such as that given in the ' Challenger ' Eeports *. I have 



* It is unnecessary to acknowledge in detail the full use I have made of the 

 published woj-ks of my predecessors and fellow-workers at the Tunicata, as I 

 have ransacked every paper known to me for lists, characters, and other hints 

 as to the affinities of those species I have not been able to examine myself. I 

 have found specially useful the recent papers of Traustedt, Sluiter, von Drasche, 

 and Lahille. 



