GASTEROPODA. 



413 



haps by some solvent quality in the saliva, the hardest shells are 

 soon perforated by this singular file. 



(448.) The salivary glands are lodged in the visceral cavity, 

 and are composed of numerous secerning cseca enclosed in a mem- 

 branous capsule (Jig. 192, A, A:) : their ducts (g, e) 9 which are ne- 

 cessarily as long as the proboscis when extended to the utmost, 

 open by two apertures placed at the sides of the spinous tongue (b). 

 The oesophagus (fig. 191, g, g) runs along the centre of the 

 proboscis throughout its entire length, and, when that organ is pro- 

 truded, becomes nearly straight ; but, when the proboscis is drawn 

 in, the oesophagus is folded upon itself among the viscera. 



Just at the commencement of Fig. 192. 



the stomach there is a small 

 crop (Jig. 192, /), and the 

 stomach itself is single, with- 

 out anything in its texture re- 

 quiring special notice ; its lin- 

 ing membrane being soft, and 

 gathered into longitudinal folds 



(0- 



Equally simple is the alimen- 

 tary apparatus of the Hetero- 

 poda. In these the stomach 

 (jig. 188, f) is a mere dilata- 

 tion of an intestiniform tube. 

 The intestine is not lodged in 

 the general cavity of the body ; 

 but, with the mass of the liver, 

 is contained in a kind of bag 

 attached to the back of these 

 singularly formed animals, and 

 in some genera, as for example 

 Carinaria, defended by a de- 

 licate transparent shell, which 

 in appearance offers a miniature 



resemblance of that of the Argonaut. It is in this visceral sac 

 that the heart and generative apparatus are likewise generally en- 

 closed ; but in many forms of the Heteropoda, both the append- 

 ed sacculus and shell are wanting, in which case the viscera are of 

 course lodged in the general cavity of the body. 



(449.) But although in Buccinum, Pterotrachea, and kindred 



