RELATIONSHIPS OF THE FIXED AND FREE TUNIC AT A. 181 



which the gemmae are permanently united in circles, and thus described in my 

 notes : — " This form presents seven perfect Salpians disposed in a circle, radiating, 

 with their posterior extremities approximated near the centre, and enveloped in a 

 common membrane, like a medusiform disc. 



" Eespiratory openings occupying one surface of the disc, the anterior or 

 orifice of ingress being marginal, and the posterior central. The testis and a 

 diverticulum of the alimentary canal forming two elongated papilliform processes, 

 projecting from the posterior extremity of each animal (but within the common 

 envelope), and convening towards the centre of the disc. Intestine forming an 

 open arch, with its convexity directed backwards, across which the long and nar- 

 row duct of the testis passes to open into the respiratory chamber. Each zooid 

 bearing a solitary embryo communicating with the sinus system, and enclosed in 

 a spherical capsule. 



" Otolithic sac rather prominent, and projecting from the under surface of the 

 ganglion. 



" ' Hypopharyngeal band,' or gill and muscular system in every respect as in 

 ordinary Salpw. 



" The arrangement of the zooid s in this case very much resembles that in Py- 

 rosoma, more especially the primary circle of the latter ; but the whole economy 

 in other respects is Salpian. Taken in the towing-net, lat. 32. 53 S., long. 

 156'00 E., and subsequently in other localities." 



OrtJiocoela (Salpa pinnata of Authors). 



It would be quite as philosophical to include the whole of the cheilostomatous 

 Polyzoa under one generic term, as to group all the strikingly diversified animals 

 of the Salpian type as mere species of the genus Salpa. Under a similar impres- 

 sion, Savigny set about the establishment of seven new genera ; but their claims 

 as such do not seem to be generally admitted by zoologists. 



With regard to the genus here under consideration, I find the following obser- 

 vations amongst my notes: — 



" While cruising in the S.W. Pacific, we frequently met with a Salpian 

 answering perfectly to the description of Salpa pinnata, though this is rather in- 

 definitely given by M. De Blainville ; and in our late voyage to the West Indies 

 in H.M.S. ' Icarus,' apparently the same species frequently made its appearance 

 in the towing-net, together with Salpa zonaria, and numerous other species. It 

 appears to me that the said S. pinnata, if I have correctly identified it, deserves 

 to be removed from the genus Salpa, and placed by itself, until other species are 

 added to it with the same generic characters. The propriety of this step, how- 

 ever, may be better seen when the principal features of the anatomy of the animal 

 have been passed in review. 



" In some instances specimens attain a length of about two inches, with a 



