SPECIAL ANATOMY. 205 



layer ; its epithelial cells are flattened, from three to six 

 sided, granular, and with large, round nuclei. 



The muscular substratum (figs. A, B, C, 2) of the 

 mucous lamina is composed of unstriped fibres, arranged 

 transversely, obliquely, and longitudinally. It is inflect- 

 ed outwards beneath the mantle, in Limax and Avion, 

 to form the outer parietes of the pulmonary chamber. 

 Between this portion and the mucous layer is placed the 

 rudimentary testa (fig. A, 6). In TehennopJwrus, it is 

 inflected inwards (fig. B, 5) beneath the anterior portion 

 of the mantle, to form the parietes of the pulmonary 

 cavity. Its transverse fibres predominate within the 

 tentaculiB, its longitudinal fibres, in the exterior pul- 

 monary parietes of the testaceous genera, and especially 

 accumulate on the outside of and parallel to the rectum, 

 so as to serve as an efficient agent in the retraction of 

 the collar, and an aid in the expulsion of mattefs from 

 the rectum. 



Interior to the musculo-mucous investment of the body 

 is a second covering, (figs. A, B, C, 3) which may be 

 considered as a sort of peritoneum. It is a muscular 

 membrane, and encloses the digestive and generative 

 apparatus. It is usually pretty closely attached to the 

 outer tegument, except in Tehennopliorus carolinensis, 

 in which the two are separated in all parts of the body, 

 except above the pedal disc, where they are firmly 

 blended together, as in all Gasteropoda. It forms the 

 partition or diaphragm between the visceral and pulmo- 

 nary cavities. This membrane is composed of transverse 



