REPORT OX THE TUNICATA. 
81 
Edwards’ section “ Polycliniens.” Giard’s memoir contributed largely to the knowledge 
of the Compound Ascidians, especially in regard to methods of gemmation, but his 
classification did not make much advance upon that of Milne-Edwards. 
Della Yalle, vniting in 1877, accepts Giard’s arrangement with one change which is of 
importance. In the Catenatse he places Diazona as a third family, the Diazonidge, in 
addition to the three, Perophoridse, Clavelinidse, and Botryllidse, recognised by Giard. 
We come now to Dr E. von Drasche, the latest authority on the Compound Ascidians, 
who, both in his preliminary note published in 1882 and in his detailed memoir on the 
Synascidise of the Gulf of Eovigno, wisely abstains from any attempt to form great 
divisions, and merely groups the genera in a series of carefully chosen families. Of 
these, the BotryUidse correspond to JMilne-Edwards’ old section “ Botrylliens,” while the 
Didemnidae and Diplosomidge are identical with Giard’s families bearing the same names. 
The Polyclinidse and the Distomidse do not correspond exactly to any of Giard’s families, 
but the former are Milne-Edwards’ “ Polycliniens ” without change. 
A new family, the Chondrostachpdae, has been formed for the reception of 
Macdonald’s Cliondrostachys and von Drasche’s Oxycorynia, remarkable forms in which 
the Ascidiozooids are all placed upon a common peduncle penetrated by large vascular 
canals. I am not inchned to admit the necessity for this new family, and a number of 
the most interesting new forms obtained during the Challenger Expedition are inter- 
mediate, I believe, between von Drasche’s Oxycorynia and Della Valle’s Distaplia, and 
so bridge over the gap between the Chondrostachyidse and the Distomidge as defined by 
von Drasche. The two remaining families of von Drasche’s system, the Clavelinidse and 
the Perophoridae, are, I consider, more closely allied to the Simple than to the Compound 
Ascidians. The 2 ;enus Diazona I regard as a connecting link between the Claveliiiidae 
and the Chondrostachyidae, and I find myself unable to decide whether it should be placed 
amongst the Simple or the Compound Ascidians. After all it is a matter of secondary 
importance where exactly the artificial line separating the two groups should be drawn. 
Several new genera have been added by the Challenger investigations, but they 
nearly aU find places in some of the above mentioned families. One of the most 
remarkable is Ccelocormus, for which a new family, the Coelocorinidse, must be instituted. 
I have added, also, a second new family, the Poly sty elidse, formed for the reception of 
Giard’s genera Polystyela and Synstyela, and some allied forms, all of which have up 
till now been regarded as Simple Ascidians, along with some new species obtained during 
the Challenger Expedition. My reasons for taking this step, and an account of the 
probable affinities of the group, will be given farther on in the Eeport (p. 322, and 
Summary). 
Dr von Drasche does not define the Synascidise, and from one or two passages in his 
memoir it seems probable that he is in very much the same position in which I now find 
myself, viz., unable to detect any character or combination of characters which will serve 
