70 
THE VOYAGE OF H.M.S. CHALLENGEE. 
Test gelatinous or cartilaginous, often thickened at the base to form a peduncle, 
which may be traversed by large canals containing the vascular appendages 
of the Ascidiozooids. 
Branchial Sac well developed ; usually no internal longitudinal bars present. 
Dorsal Lamina in the form of languets, rarely a plain membrane. 
Alimentary Canal placed at the posterior end of the branchial sac. 
Reproductive Organs in the intestinal loop, or alongside it. 
I use this family name in a somewhat different sense to that in which it has been 
employed by previous writers. Giard considered that the family Distomidse contained 
three genera — Distoma, Diazona, and Sigillina. The last named form I regard as 
one of the Polyclinidse, and Diazona seems to be a connecting link between Chon- 
drostachys and Clavelina, and is therefore extremely difficult to place. Perhaps the best 
way might be to leave it, as Della Valle placed it in 1877, in a distinct family by itself. 
This reduces Giard’s Distomidse to the genus Distoma. . To this Della Valle added 
Distaplia in 1881, and in von Drasche’s classification (1883) we find the family 
Distomidse consisting of these two genera with the addition of a subgenus of Distoma, 
viz., Cystodytes. In a distinct but adjacent family, the Chondrostachyidse, he places 
Macdonald’s Chondrostachys and his own Oxycorynia, both interesting forms. So far 
as I can make out from von Drasche’s definitions and descriptions, he distinguishes the 
two families upon the rather slender ground that in the Chondrostachyidse the colony 
is supported upon a peduncle traversed by canals, while in the Distomidse this is not 
the case, but the Ascidiozooids are provided with vascular ectodermal appendages. 
Now in the Challenger collection there are a considerable number of forms which are 
allied to Distoma and Distaplia in certain characters but they have peduncles, in some 
cases long and in others short, and these peduncles are traversed by canals, which, 
however, contain vascular appendages prolonged downwards from the posterior ends of 
the Ascidiozooids. Hence it is perfectly obvious that these forms, to which I have 
;given the generic title Colella, unite the characters of the Chondrostachyidse and the 
Distomidse, and consequently render it impossible any longer to separate the two 
families. I have retained the older name, derived from what has all along been 
considered as the central form of this group, viz.. Distoma, but the family has now 
much wider limits than it has had hitherto, and embraces at least the genera — 
Chondrostachys, Macdonald, Oxycorynia, von Drasche, Colella, Herdman, Distoma, 
Gaertner, Cystodytes, von Drasche, Distaplia, Della Valle, and, probably, Symplegma, 
Herdman. Whether or not Diazona, Savigny, should be added must be left doubtful. 
The general form of the colony throughout the family is very variable, but usually it 
is of large size. Sometimes it is an irregularly rounded mass (as in Distoma crystallina) , 
occasionally it is a more or less incrusting layer (as in Cystodytes draschii) ; while very 
