156 BULLETIN" 100, UNITED STATES NATIONAL MUSEUM. 



the Doliolidae form complete rings, while in the Salpidae they are 

 said to form incomplete rings : the animals of the former group being 

 called Gyclomyaria (Gegenbaur), those of the latter group Hemimyaria 

 (Herdman). Of course in many species of Salpidae, as Brooks 

 (1893) long ago clearly showed, the muscle bands are complete. I 

 suggest as preferable terms Multistigmosa for the Doliolidae, in which 

 the pharyngeo-cloacal partition contains numerious stignata, and 

 Astigmosa for the Salpidae, in which this partition has been reduced 

 to a single axial rod, no stigmata being present. 



Probably ancestrally the form and musculature of Salpa resembled 

 somewhat that of Doliolum which, in the character of the stigmata 

 and the relations in the nervous system, is more primitive than 

 Salpa. Probably the primitive muscle schema consisted of a series 

 of strong hoop-like bands around the body (the body muscles), and 

 a series of more delicate sphincters at both the oral and atrial aper- 

 tures. The body muscles in some of the Salpidae are still much in 

 this condition, especially in the solitary individuals. 



In the more aberrant subgenera of the Salpidae we observe a 

 reduction in the musculature. In most species the aggregated zooids 

 show fewer body muscles than do the solitary zooids of the corre- 

 sponding species. Four is the usual number of the body muscles in 

 the aggregated zooids of the Cyclosalpas (three in C. fioridana), five 

 the number in the aggregated zooids of all other species except 

 Ritteria hexagona (six), the Thalias (four), Pcgea (four), and Trau- 

 stedtia (three or four, according to interpretation). The intermediate 

 muscle is somewhat reduced in the Thalias, and is greatly reduced in 

 Thetys, Pegea, and Traustedtia. In the solitary forms, reduction of 

 the muscles is less usual, but in its extreme, in Pegea, is very marked. 

 In the Cyclosalpas the solitary individuals show seven body muscles. 

 In the Ritterias the number is large, being variable in at least some 

 of the species. In the Apsteinias and the Salpas the number is 

 eight or more. In Iasis the number is five. Thetys shows a very 

 large number, confined however to the dorsal half of the body. 

 Thalia has five, while Traustedtia and Pegea have but four developed 

 as body muscles and these very short, especially in Pegea. 



The atrial musculature in the Cyclosalpas conforms to the sup- 

 posed ancestral schema and there is great departure from this 

 schema among the Salpidae only in the subgenera which have 

 modified the atrial siphon into a strongly two-lipped structure in 

 which the upper lip is developed as an overhanging valve, that is, in 

 Iasis and Thalia. The atrial retractor muscle is not readily recog- 

 nized in some species with cylindrical atrial siphon (Cyclosalpa 

 pinnata, pi. I, fig. 1, a. r.) though in others it is well developed 

 (C. vlrgula, pi. 11, fig. 26). In more modified species the atrial 



