vol. 2, pt. 2.] A TAXONOMIC STUDY OF THE SALP1DAE METCATF. 115 



U.z, 



i.m. 



runs obliquely upward and backward, past the oral retractor muscle, 

 and stops before reaching the dorsal surface. The anterior division 

 follows the same course, but ends just short of the oral retractor mus- 

 cle. The basal sphincter of the upper lip (u. 3) is a broad band 

 which at first sight seems to be a continuation dorsally of the ante- 

 rior division of the intermediate muscle. Closer inspection, however, 

 shows it to be distinct from, though it abuts upon, the intermediate 

 muscle. The short oral retractor muscle is continued forward into 

 the first and second sphincters of the upper lip and the first and third 

 sphincters of the lower lip. The second and fourth sphincters of the 

 lower lip are united at the angle of the mouth, lying a little ventral 

 to the oral retractor. They might be said to form a very short ven- 

 tral division of the oral retractor muscle. 



The cloacal musculature (fig. 109) differs in different individuals. 

 My specimens from the eastern and u. 3 



western Pacific Ocean (A) agree with 

 Streiff's description (D), except as 

 to the internal or external position 

 of the overlapping muscles. Those 

 from the Atlantic coast of New Eng- 

 land (B and C) present slightly di- 

 vergent conditions, none of which 

 agrees exactly with the Pacific speci- 

 mens, though some differ only mi- 

 nutely. For the Pacific type I copy 

 Streiff's figure, modifying only the 

 overlapping of the muscles, which I 

 find not as Streiff shows. For the 

 New England coast specimens I 

 twice again modify Streiff's figure 

 to show two of the several variants, 

 one of which (C) most nearly ap- 

 proaches the Pacific type, and another (B) which is more unlike the 

 Pacific specimens. In general the internal or external position of 

 muscles which overlap is constant in other species of Salpidae. It 

 is therefore a little surprising to find discrepancy in this regard be- 

 tween Streiff's specimens and mine. The divergence in the group- 

 ing and attachment of the muscles is no more than might be expected 

 in this very widely distributed and very abundant species. It is of 

 some interest that in my very abundant material from both the 

 Atlantic and Pacific Oceans, the Atlantic animals should show con- 

 siderable diversity in the cloacal muscles, while the Pacific animals 

 show almost none. 



The gut is more compact than in the solitary form. The endostyle, 

 in both solitary and aggregated forms, is confined to the anterior 



mi. 



Fig. 108. — Thalia democratica, aggregated 

 form, oral muscles of the right side 

 seen from within. streiff (1908). 



