CLA.SSTFICATIO]Sr OF THE TIJNICATA.. 561 



also, after the authorities for the species, given in brackets a 

 brief indication of the geographical distribution of each species, 

 and have there made use of the following contractions : — 

 N. Atl. (North Atlantic); S. Atl. (Soutli Atlantic) ; N.W. Eur. 

 (the north-western coasts of Europe, such as British area, Danish 

 seas, &c.) ; E. N. Am. (the eastern coast of North America) ; 

 Arct. (the Arctic seas) ; W.Ind. (the West Indies) ; Med. (the 

 MediteiTanean, including the Adriatic) ; Eed S. (the E,ed Sea) ; 

 Ind. 0. (the Indian Ocean); Mai. (the seas of the Malay Archi- 

 pelago) ; Austr. (the coasts of Australia) ; A. Arct. (the Ant- 

 arctic) ; Mag. (Straits of Magellan and the neighbourhood) ; 

 S. Pac. (South Pacific) ; N. Pac. (North Pacific Ocean) ; and 

 Jap. (Japanese Coast). 



TUNICATA, LamJc., 1816. 



This class is divided into three Orders, the Ascidiacea, the 

 Thaliacea, and the Larvacea. 



Order I. ASCIDIACEA, Bh., 1827. 



This group includes fixed or free-swimming Simple or Com- 

 pound Ascidians, which in the adult are never provided with a 

 tail and have no trace of a notochord. The free-swimming 

 forms are colonies, and the simple Ascidians are never free- 

 swimming. 



The test is permanent and Avell developed; as a rule it 

 increases with the age of the individual. 



The musculature of the mantle is in the form of an irregular 

 network, there being no regular circular bands. 



The branchial sac is large and well developed. Its walls are 

 perforated by numerous slits (the stigmata) opening into a single 

 peribranchial cavity, which communicates with the exterior by 

 the atrial aperture. 



The anus opens into the peribranchial cavity. 



Many of the forms reproduce by gemmation, and in most of 

 them the sexually produced embryo develops into a tailed 

 larva. 



