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chambers. Each respiratory chamber extends along the side of the liver case 

 from the slit between the lateral arc of the collar and the lateral siphonal valve — 

 which , it will be remembered , lies on the side of the liver case a short dist- 

 ance behind the head and forms the hind boundary of the neek , — to the. long, 

 longitudinal slit between the mantle and the body and siphonal retractor. Each 

 gill arises from the side of the body at the level of the origin of the siphonal 

 retractors and, passing outside this muscle, extends foi'ward in the respiratory 

 chamber to the lateral siphonal ^■alve. A fold of integument forms a mesentery 

 which attaches the gill along its whole length to the mantle. Water entering 

 the mantle passes between the lateral siphonal valves and the mantle , over and 

 through the gills , and then enters the cloacal chamber which extends from the 

 right and left compartments of the hind end of the chamber , forward to the 

 inner opening of the .siphon . through which the water escapes to the exterior. 



The rectum emerges from the lower surface of the body at the level of 

 the base of the gill , and extends forward to the proximal opening of the siphon. 

 A nephridial pore opens through the rounded lower wall of the viscera at a 

 point midway- between the base of the rectum and the corresponding portion of 

 the siphonal retractor. In the female . the openings of the nidamental and acces- 

 sor}^ nidamental glands lie a short distance behind the nephridial pore. The 

 oviduct passes under the base of the gill and emei-ges from the visceral mass 

 into the cloacal chamlier between the rectum and the left siphonal retractor. It 

 ends a short distance behind the tip of the rectum. In the male, the penis 

 occupies a corresponding position. The genital sac, which Marchand believes to 

 be homologous with the nidamental gland of the female, opens into the mantle 

 chamber on the outer side of the penis beneath the base of the gill. 



