GEOGRAPHY, ETC.^PHYLOGENY. 
Tun. 5 
Ascidianfc are apparently much more abundant in the southern than in 
the northern hemisphere. The bathymetrical range of the ‘ Challenger ’ 
Compound Ascidians is from the shore down to 1600 fath. ( Pharyngo - 
dictyoh mirabile) ; comparatively few species, however, extend into the 
Abyssal zone, and the Ascidice Compositai must be regarded as mainly a 
shallow- water group. 
In the Report on the Fauna of Liverpool Bay, Herdman (5) records 
47 species of Tunicata from the L. M. B. C. district, of which 2 are new 
to science and 7 new to the British seas. 
Giard (3) records a Diazona , which he considers identical with D. 
hebridica , Forb. & Goods, from the south-east coast of Brittany. He also 
finds Distaplia rosea, Della Yalle, and from an examination of it has 
come to the extraordinary conclusion that it is the fixed representative of 
the pelagic forms Doliolum and Anchinia ! 
Roule (19) records 14 species of Ascidiulce from the coasts of Pro- 
vence. He gives tables (pp. 257 & 258) showing the geographical distri- 
bution of these species, and also their distribution according to depth 
and the nature of the bottom. 
Yon Drasciie (2) records 5 species of Simple Ascidians, 2 of them new 
to science, from Jan Mayen. 
Phylogeny. 
Herdman (7) discusses the probable origin and course of evolution of 
the various groups of the Tunicata . He considers that the Proto-Tunicata 
were derived from the Proto -Chordata, and are now represented by the 
Larvacea ( Appendiculariidce ). The Proto- Thaliacea and the Proto - 
Asculiacea were two divergent branches from the Proto-Tunicata , tho 
former of which broke up into the Cyclomyaria ( Doliolidce ) and the 
Ilemimyaria ( Salpidai ). The Proto- Ascidiacea which became fixed and 
modified are represented now by the Clavelinidce , from which the various 
groups of Simple and Compound Ascidians have been derived. The 
Compound Ascidians are regarded as a polyphyletic group derived from 
the ancestral Simple Ascidians at three distinct points. The Ascidice 
Salpiformes ( Pyrosoma ) are considered as being allied to tho Compound 
Ascidians through Ccelocormus, and have no direct connection with the 
Thaliacea. 
A more detailed phylogeny of the families of the Ascidiai Compositai , 
showing the positions and genetic relations of the new ‘ Challenger ’ 
forms, is given in (4), at p. 387. 
Lahille (10) proposes a new classification of the Tunicata. He first 
divides them (following Balfour) into Perennichordata (the Larvacea of 
Herdman) and Caclucichordata (the Thaliacea and Ascidiacea of Herd- 
man), and then subdivides the latter, according to the condition of the 
branchial sac, into — (1) Aplousobranchiata (including Salpa , Doliolum, 
and apparently Pyrosoma and some families of the Compound Ascidians, 
such as the Diplosomidai , the Didemnidai, and the Polyclinidce ) ; (2) 
Phlebobranchiata (including Diazona and some of the Clavelinidce , and 
the Asculiidce) ; (3) Stolidobranchiaia (including the Cynthiidce , the 
Molgulidce, and the Botryllidm). 
