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



97 



usual way, its posterior branch, on each side, passing to the base of 

 the atrial siphon. Behind the siphon, at its base, these posterior 

 branches are contiguous or may unite, forming a single band, which 

 runs to one side of the broadly conical mantle tube that enters the 

 asymmetrical posterior protuberance from the body. The united 

 portion of these muscles doubtless corresponds to the visceral muscle 

 of the Cyclosalpas. 



The intermediate muscle is reduced (fig. 83), lying well down on 

 the side of the body, at the base of the oral siphon. Its anterior end 

 runs to the base of the anterior protuberance of the mantle. Its 

 posterior end approaches, but does not unite with, the first body 

 muscle. It is associated with the oral muscles, rather than the body 

 muscles. 



i.m. 



Fig. 85. — Salpa cylindrica, aggregated zooid, oral muscles, laevo-dorsal view. The test is 



OMITTED. 



The oral muscles (fig. 85) consist of a well-developed oral retractor 

 which gives rise antero-dorsally to three sphincter muscles on each 

 lip, the arrangement of these muscles being a complicated one. A 

 lew postero-dorsal strands of the retractor are continued into the 

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

 the lower lip. The second sphincter of the upper lip is short, extend- 

 ing only a little beyond the angle of the mouth. The antero-ventral 

 strands of the oral retractor divide into two sets of fibres, an internal 

 set, which bend sharply back to form the broad third sphincter of 

 the upper lip, and an external set, which immediately divide into 

 two groups to form respectively the second and third sphincters of 

 the lower lip. 



