Agassiz.] 18 [June 20, 



History. As he has given no description, either of the chain or soli- 

 tary form, it may not be out of place to describe our species, and 

 point out its relations to other known species. The chains and soli- 

 tary individuals make their appearance during the end of Juiy, and 

 have been found from that time till the end of October. The chains 

 move along with the current, seemingly quite helpless, though the 

 upper extremity is sometimes deflected somewhat abruptly by at- 

 tempts to escape capture. The solitary individuals, on the contrary, 

 are exceedingly active, swimming about vigorously, generally with the 

 anterior extremity uppermost ; expelling (through the posterior ex- 

 tremity) 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 powerful 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 has 

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

 found, the ventral, while the anterior and posterior extremity corres- 

 pond to the openings through which the water is introduced into the 

 body, and expelled from It, thus homologizing the Salpa completely 

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

 soUtaria of the Salpa Cahotti Des. (figs. 1-3) resembles that of the 

 Salpa spinosa Ott., figured by Sars In his Fauna Littoralis, but differs 

 from it materially, as the subsequent observations will show. The body 

 is transparent, almost colorless, perfectly smooth, with the slightest pos- 

 sible tinge of pink, increasing in intensity towards the posterior ex- 

 tremity ; the nucleus Is of a deep chesnut color. The general outline 

 of tke body when seen from the dorsal (fig. 1), or fi-om the ventral 

 side (fio-. 2), is barrel-shaped, with a uniform curvature at both ends. 

 The posterior extremity terminating in two long conical processes 

 (p.p.) with a coecum of the respiratory cavity (c.c.) at the base 

 (fig. 1). When seen In profile (fig. 3), it is truncated abruptly at the 

 two ends, from the ventral to the dorsal side ; the extremities are 

 slightly convex ; the posterior truncating plane is more Inclined than 

 the anterior, and as the dorsal side Is at the same time somewhat 

 convex, this gives the anterior end a slightly pointed appearance. 

 Besides the two large posterior conical processes, there are two sharp 

 lateral ones, quite small (I. p.), and seen only from the ventral side 

 (fig. 2) on each side of the termination of the respiratory cavity, and 

 two other short processes (o.p.) situated on the median line (fig. 2) 

 at the posterior extremity of the body, placed one above the other 

 (figs. 1 and 3), the larger process is situated nearest the posterior 

 opening. These processes, like the surface of the body, are quite 

 smooth. There are six muscular bands entirely encircling the body ; 



