MOLLUSCA. 51 



The muscular envelope of the animal has been separated 

 from the foot proper along the left side, and turned over to the 

 right, together with the shield-shaped mantle, heart, and pul- 

 monary sac. The digestive tract and the glandular organs 

 in connection with it have been displaced from their natural 

 positions and pinned to the tablet on the left side of the prepa- 

 ration, while the generative organs, similarly displaced, occupy 

 the right side. The superior tentacles have been pinned by 

 their retractor muscles in front of the animal's head. 



On the left side of the head are the salivary glands, two 

 lobulated organs connected with the mouth by two ducts which 

 pass forwards through the nerve-collar and pierce the buccal 

 mass anteriorly to it. The glandular mass which encircles the 

 anterior margin of the buccal mass is 'Semper's organ,' sup- 

 posed by its discoverer to be olfactory. 



The oesophagus, emerging from the buccal mass, passes 

 through the nerve-collar, and almost immediately expands into 

 a long fusiform stomach, the posterior segment of which, 

 separated from the anterior three-fourths by a slight constric- 

 tion, receives the two biliary ducts, one from each of the two 

 principal lobes into which the liver is divided. A convoluted 

 intestine succeeds the stomack, passing to the middle line of the 

 body, where, after a short retrograde course posteriorly, it bends 

 sharply upon itself, ascends, and terminates at an anus situated 

 on the right side of the respiratory aperture. 



In the upper portion of the specimen, and on the right side, 

 is seen the reticulated structure of the roof of the pulmonary 

 sac, the floor having been removed. 



A little posterior to this point is seen the bilocular heart, 

 together with portions of the two trunks into which the aorta is 

 divided. Beneath the heart is the sub -triangular yellow kidney. 

 In the natural position of these parts the kidney would of course 

 overlie the heart. Immediately posterior to the buccal mass, 

 and encircling the oesophagus, is the nerve-collar, consisting, 

 superiorly, of the two cephalic ganglia connected with each other 

 by a broad commissural band, and inferiorly of the parieto- 

 splanchnic and pedal ganglia. The supra-cesophageal and sub- 

 cesophageal masses are mutually connected by a double commis- 

 sural strand embracing the gullet. 



4-2 



