56 



TERRESTRIAL AIR-BREATHING MOLLUSKS. 



table, and contractile investment consists of an actively secreting mucous 

 membrane (Figs. 5, 6, 7, 1) with a substratum of interlaced muscular 

 fibres (2}. In the naked genera it is pretty uniformly developed 



Fig. 5. 



1 2 S 



Fig. 5 is a diagram representing the disposition of the coverings of the body in Limax and Arion. 

 1, mucous lamina; 2, muscular substratum; 3, muscular peritoneum ; U, visceral cavity ; 5, rudiment- 

 ary testa ; 6, pulmonary chamber. 



throughout, but is thickest upon the pedal disk, the tail, and the upper 

 surface of the mantle, and thinnest upon the head, eye-peduncles, and 

 reflected border of the mantle. 



Fig. 6. 



Fig. 6, disposition of the tegumenta in Tebennophorus. 1, mucous lamina; 2, muscular lamina; 

 S, peritoneum ; A, visceral cavity j 5, pulmonary chamber ; 6, interval between the two muscular 

 layers. 



In the testaceous genera, upon the part of the body corresponding to 

 the interior of the shell, it appears as if the mucous layer had been 

 pushed downwards to form the collar (Fig. 7, 1*)', but it may be still 

 traced over the surface of the turbinated portion, as a delicate, tessel- 

 lated epithelium. 



The mucous glands are very numerous in the mucous layer; its 

 epithelial cells are flattened, from three to six sided, granular, and with 

 large, round nuclei. 



The muscular substratum (Figs. 5, 6, 7, 2) of the mucous lamina is 

 composed of unstriped fibres, arranged transversely, obliquely, and lon- 

 gitudinally. It is inflected outwards beneath the mantle, in Limax and 

 Arion, to form the outer parietes of the pulmonary chamber. Between 



