DIGESTIVE ORGANS. 33 



or cylindrical or clavate as in Pleurotoma, Littorina, Trochus, 

 etc. Sometimes, as in Dolium, Cassis and Triton, the elongated 

 glands are in two subdivisions, divided by a deep fissure into a 

 small anterior and a larger posterior portion (pi. 4, fig. 27). 

 The two glands may also unite over the dorsal side of the oesoph- 

 agus, into a single mass, from which, however, separate ducts 

 proceed on either side. 



Souleyet was not able to discover distinct salivary glands in 

 Turbo, but its oesophagus is enlarged just behind the mouth, and 

 this enlarged space is furnished with a number of folds which 

 may be regarded as substitutes (pi. 4, fig. 34). 



In Conns there is only a single gland (pi. 4. fig. 36 , and it is 

 veiy doubtful whether this is salivary in function; Troschel 

 considers it a poison-gland. 



In addition to the salivary glands there is found in Murex 

 (not observed in other genera), a gland lying above the oesoph- 

 agus ; it is thick, granular in structure, of liver-brown color, 

 divided into several large lobes and opens into the oesophagus by 

 two ducts. Its purpose is unknown. In Dolium the secretion 

 of the salivary glands is distinctly acid, a property first detected 

 by Troschel, and afterwards observed in this and in several 

 other mollusks by a number of investigators.* Troschel states 

 that if the Dolium galea is irritated, it will protract its proboscis 

 as much as a foot, and eject from it a quantity of clear fluid, 

 with a very acid smell, and producing effervescence upon calca- 

 reous soil. The liquid has been ascertained to contain several per 

 cent, of free sulphuric acid, and about 4 per cent, of hydrochloric 

 acid.f How the mollusk secretes this acid, and how it protects 

 its own tissues and the epithelial cells of the glands themselves 

 against its action is not at all understood. The acid secretion 

 does not appear to be taken into the stomach, for Troschel 

 found in the stomach of Dolium seaweed and calcareous remains, 

 which, when artificially brought into contact with the acid, im- 

 mediatelv commenced to dissolve. He thinks the secretion is 



* Researches upon the organs which, in the gasteropods, secrete sulphuric 

 acid. By Prof. Paolo Panceri, Jour, de Conch., 3d ser., ix, 308, 1869. 



f De Luca and Panceri have ascertained the existance of free sulphuric 

 acid in the salivary product of Murex trunculus and M. brandaris. Ann. 

 8c. Nat., 87, 1867. 



