334 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



not act as a retractor for the tentacles. It is closely con- 

 nected with the longitudinal muscles of the stalk, both mor- 

 phologically and functionally. The somatic portion together 

 with the peduncular portion contracts the whole polypide 

 upon the ventral side, forming the characteristic bow-shape 

 so commonly assumed. The correlation of muscular devel- 

 opment exhibited by Myosoma depends primarily upon the 

 growth of the ventral muscle. Its action is antagonistic to 

 that of the lophophoral sphincter; hence there follows the 

 unusually strong development of the latter. In contraction, 

 the ventral muscle draws the tentacular disc and the dorsal 

 organs toward the ventral side. This would greatly dimin- 

 ish the space within the atrial cavity, which at certain seasons 

 of the year, as when embryos are rapidly developing, would 

 be a disadvantage. By the correlated growth of the atrial 

 retractors the floor of the atrium is drawn downward and 

 the space within is, in a measure, preserved. 



Such muscles as are usually found in the calyx of the 

 Pedicellinidse, viz., the sphincter muscles, the tentacular 

 muscles, and the body muscles mentioned by Ehlers for 

 Ascopodaria niaci'opus, are said to originate from the paren- 

 chymatous tissue of the calyx. It is difficult to conceive 

 that such alone is the origin of the muscles of the calyx of 

 Myosoma. In examining sections of the calyx, the assump- 

 tion that the muscle fibers in the body arise in great part 

 from those of the stalk, and that many of them have become 

 secondarily divided, does not seem unreasonable. Such a 

 hypothesis, however, can only be established by a study of 

 the development of the polypide. 



It is the open communication between the stalk and calyx 

 of Myosoma which allies it so closely with Loxosoma. In 

 the latter, the line of demarcation between body and stalk 

 is not well defined. The muscle fibers of the stalk pass 

 directly into the body, and, according to most observers, 

 end somewhere in the lower part of the latter. In his ac- 

 count of Loxosoma kefersteinii, Nitsche (1869) says that the 

 muscle fibers of the stalk are attached to the base of the 

 stomach. Vogt (1876) in describing L. phascolosomatum 



