6 SALPIDiE. 



Salpa Caboti.* 



Salpa Caboti, Desor, Proc. Bost. Soc. Nat. Hist. iii. 75 (Oct. 1848), no descr. — 

 Alex. Agassiz, from the same, xi. 17, Fig. 1-5 (Dec. 1866). — Stimpson, Check 

 Lists, 1. 



The Salpa here described is quite common south of Cape Cod in 

 Vineyard Sound, Buzzard's Bay, and Long Island Sound. I sup- 

 pose it to be the species named by Desor, Salpa Caboti, mentioned 

 in the third volume of the Proceedings of the Boston Society of 

 Natural History. As he has given no description, either of the 

 chain or solitary form, it may not be out of place to describe our 

 species, and point out its relation to other known species. The 

 chains and solitary individuals make their appearance during the 

 end of July, and have been found from that time till the end of Oc- 

 tober. The chains move along with the current, seemingly quite 

 helpless, though the upper extremity is sometimes deflected some- 

 what abruptly by attempts to escape capture. The solitary individ- 

 uals, on the contrary, are exceedingly active, swimming about vig- 

 orously, generally with the anterior extremity uppermost, expelling 

 (through the posterior extremity) by quick and powerful jerks the 

 water which propels them by its reaction. Their motions are very 

 similar to those of Trachynema ( Circe^ ; they can readily change 

 the direction of their movements, and regulate them by their pow- 

 erful transverse muscular bands, though they lack in their motions 

 the ease and grace of Jelly-Fishes. 



In describing this Salpa, the side on which the heart is placed is 

 called the dorsal ; the opposite, on which the nervous ganglion is 

 found, the ventral ; while the anterior and posterior extremity cor- 

 respond to the opening through which the water is introduced into 

 the body, and expelled from it, thus homologizing the Salpa^ com- 

 pletely with the fixed Ascidians to which they are so closely related. 

 The proles solitaria of the Salpa Caboti, Des. (Figs. 1-3), resembles 

 that of the Salpa spinosa, Ott., figured by Sars in his Fauna Litto- 

 ralis, but differs from it materially, as the subsequent observations 

 will show. The body is transparent, almost colorless, perfectly 

 smooth, with the slightest possible tinge of phik, increasing in in- 

 tensity towards the posterior extremity ; the nucleus is of a deep 

 chestnut color. The general outline of the body when seen from the 



* Mr. Alexander Agassiz has kindly furnished me with the woodcuts used hy the Bos- 

 ton Society of Natural History. His description is here copied in full. 



