cla.ssificatio:jt of the tunicata. 559 



diffei'eutiate, so fiir as cau be done in tabular form *, uuder eacli 

 genus tlie numerous species not represented in the ' Challenger ' 

 Collection. 



There has never been any sufficiently compreliensive work 

 on the Tunicata describing all the known species, and although 

 this present classification and series of tables cannot pretend 

 to be such a revision, still it may be useful as a preliminary 

 essay in that direction, clearing the ground and marshalling 

 the species in groups. I can scarcely hope that my system 

 of classification will commend itself at all points to my fellow- 

 workers : in the primary divisions and subdivisions, however, I 

 have made practically no change upon the ' Challenger ' system, 

 which has been adopted by most writers on the Tunicata since. 

 Still less can I hope to have escaped error in the enume- 

 ration and arrangement of the numerous species. The literature 

 of the Tunicata is so scattered, and many of the descriptions 

 so meagre or even misleading, that it is very difficult in the 

 first place to collect the literary material, and in the second 

 place to arrange it correctly. The first to attempt this work 

 in a group is pretty sure to commit sins both of omission 

 and of commission, but may reasonably hope for lenient treat- 

 ment from his critics. I shall be very glad to receive and 

 acknowledge corrections and additions to the lists. 



I desire to acknowledge with cordial thanks the very efficient 

 assistance I have received from two advanced students of 

 University College, Liverpool, Miss A. E. Warham, B.Sc, 

 and Miss J. H. AVillmer, who, while working in my laboratory 

 during the past year, have prepared for me microscope specimens 

 and drawings of a very large number of Ascidians. Miss "Warham 

 especially has devoted a great deal of time to sectionizing nume- 

 rous colonies of Compound Ascidians ; and both Jadies have 

 undertaken a part of the laborious work of looking-up references, 

 of collecting together the various species of the genera and 

 of comparing the characteristics given by diflerent authors, 

 and so have enabled me to complete the tables much sooner than 

 with my very limited leisure would otherwise have been possible. 



Although a linear classification, such as this of necessity is, 



* Occasionally the characters made use of in some of the tables are not quite 

 satisfactoi-y. It is not possible in all cases to distinguish allied species by 

 one or two characteristics briefly put. They will serve, however, to indicate 

 which original descriptions should be consulted. 



