MOLLUSCA. 45 



Class GASTEROPODA. 

 Order 1. Opistho-lranchiata. 



73. A Sea- Hare (Aplysioi), dissected to shew the general 

 disposition of its organs. 



In the upper of the two specimens on the tablet the rudi- 

 mentary shell has been displaced to the right side of the 

 animal, and the left mantle-lobe deflected, thus exposing the 

 heart, branchia3, and terminal segment of intestine. 



The arborescent branchiae, protected by the rudimentary 

 shell, are situated behind the heart and towards the rear of 

 the body (hence the position of the animal in the order 

 Opistho-branchiata), but in front of the anus, into which a 

 black bristle has been inserted. A black bristle has also been 

 placed under the bilocular heart and the rectum. 



In the lower preparation, the muscular envelope of the 

 animal has been separated from the foot along the left side, 

 and reflected to the right, together with the heart, branchiae, 

 and parts of the generative system. The digestive tract has 

 been arranged mainly on the left side. 



The ribbon-like salivary glands (two in number) have been 

 pinned to the left of the animal's head. Posteriorly to the 

 buccal mass the oesophagus is seen communicating with the 

 stomach, which is divided by certain constrictions into three 

 compartments, the last of which, from the muscularity of its 

 walls, has been termed a gizzard. Surrounding the gizzard 

 and communicating with it by a large duct is the liver. The 

 intestine, on emerging from the liver, curves round the lower 

 border of the specimen, and passes to the anus. On the ex- 

 terior of the liver is the hermaphrodite gland, a white, irregu- 

 larly shaped, granular mass. From it a slightly convoluted 

 hermaphrodite duct passes forwards to the albuminiparous 

 gland; and after this junction and the reception of the duct of 

 a minute vesicle (seen near the anterior margin of the gland), 

 the duct passes upwards as a much larger tube to its external 

 opening, prior to reaching which it communicates with a 

 globular spermatheca. A little to the right of this part are 

 the heart and branchiae. A bristle has been placed under the 

 former. 



