VII 



MOLL USGA—MUSGULA TUBE 



123 



in the Liiiuu-iniihc, but dorsal in the Cavoliniidcc, in which family the body, as 

 compared with the head, seems to have been twisted through an angle of 180' 

 (p. 80). The muscle divides anteriorly into two lateral branches, which radiate 

 out into the fins. 



3. Pulmonata. 



In the sliell-bearing Pulmonata, the columellar muscle is strongly 

 developed. It is paired, and attached 

 at one end by many roots to the foot, 

 behind the buccal mass, and at the 

 other to the columella of the first coil 

 or whorl of the shell. It gives off' 

 three subsidiary branches — (1) the 

 retractor muscles of the optic and 

 other tentacles ; (2) the retractors of 

 the buccal mass ; (3) muscles running 

 to the viscera. 



Fig. 10".— Shell of Helix, in longitudinal 

 section through tlie columellar axis (after 

 Howes). c, Columella ; nn, columellar 

 muscle ; p, edge of oral aperture (peritreme). 



In the Daudchardia and Testacelluhe, in 

 which the dwindling visceral dome with the 

 shell which covers it have shifted to the 

 posterior end of the body, and in which all 

 possibOity of the retraction of the body into 

 the shell has ceased, only parts of the colmnellar muscle are retained, and naturally 

 those parts which are still functional. In the Daudebardia and Tcstaccllidcc these 

 are the retractors of the tentacles, and in Daudchardia the retractors of the pharynx. 

 The tentacular and pharyngeal retractors are distinct. 



The retractors of the tentacles, in Daudebardia rufa, run back separately to the 

 base of the visceral dome, not entering it, but fusing witli the body wall on each 

 side of it. In D. saulcyi the retractors do not run so fqr back, but the two on the 

 right fuse with the two on the left, and pass into the pedal musculature in the 

 anterior half of the body. The same is the case in the Testaccllidu:. 



The Retractors of the Pharynx. — In Daudebardia rufa there are found, attached 

 to the pharynx, two retractors, which, passing through the oesophageal nerve ring, 

 fuse to form one muscle,. which runs back along the base of the pharyngeal cavity 

 somewhat to the left, then ascends in the visceral dome to be attached to the 

 columella of the last coil of the shell. In D. saulcyi, where there is no projecting 

 visceral dome, and the shell merely covers a mantle cavity, the oesophageal re- 

 tractors, which are not in this case fused together, no longer run up into the shell, 

 but end in the middle of the body, where they enter the pedal musculature. 



The numerous oesophageal retractors which, in Testacella, are arranged in two 

 asymmetrical rows, cannot for several reasons be considered as the remains of a 

 columellar muscle. 



Oncidium when adult has neither shell nor columellar muscle, but its shell- 

 bearing larva also possesses a columellar muscle. 



C. Seaphopoda. 



In Dentaliwrn (Fig. 101, p. 113) two closely contiguous muscle 

 bands run on each side along the anterior side of the body, and are 

 attached anteriorly to the dorsal end of the tubular shell. At the 



