42 



with the long axis antero-posterior, and the branchial and 

 atrial apertures nearly terminal . The test is well developed. 

 The musculature of the body-wall is in the form of a series 

 of transversely-running bands, which do not form complete 

 independent rings, as in the Cyclomyaria. The branchial 

 and peribranchial cavities form a continuous space in the 

 interior of the body, opening externally by the branchial 

 and atrial apertures, and traversed obliquely from the 

 dorsal and anterior end to the ventral and posterior by a 

 long, narrow, vascular band, which represents the dorsal 

 lamina, the dorsal blood sinus, and the neighbouring part 

 of the dorsal edge of the branchial sac of an ordinary 

 Ascidian. The alimentary canal is placed ventrally. The 

 embryonic development is direct, no tailed larva being 

 formed. 



The Salpidfe, the chief family in this sub-order, includes 

 the single genus Salpa, which, however, may be divided 

 into two well-marked groups of species — (1) those, such 

 as S. plnnata, in which the alimentary canal is stretched 

 out along the ventral surface of the body, and (2) those, 

 such as S.fiisiformis, in which the alimentary canal forms 

 a compact globular mass, the "nucleus," near the posterior 

 end of the body. About fifteen species altogether are 

 known; they are all pelagic forms, and are found in many 

 seas. Each species occurs in two forms — the solitary 

 asexual (proles solitaria) and the aggregated sexual (p)-oles 

 gregaria) — which are usually quite unlike one another. 

 The so'itar}^ form gives rise, by internal gemmation, to a 

 complex tubular stolon, which contains processes from 

 all the more important organs of the parent body, and 

 which becomes segmented into a series of buds. As the 

 stolon elongates, the buds near the free end, which have 

 become advanced in their development, are set free in 

 groups, the members in which remain attached together 



