110 DESCRIPTIONS OF PREPARATIONS. 



with the skin of the dorsum leaving only the small pulmonary aperture. Its 

 floor is thickened and muscular, and represents that portion of the general 

 integument which is roofed over by the fold of the mantle. The heart, 

 composed of a thin-walled auricle and thick-walled ventricle, is seen as in 

 dextral Molluscs, on the left side, and below it lies in this preparation the 

 triangular pale-coloured kidney. The vessels have been injected with a 

 red-coloured fluid from the auricle. The right half of the roof of the 

 pulmonary chamber is covered by vascular ramifications : the anterior part 

 of the left side is smooth ; its posterior portion corresponds to the pericar- 

 dium and kidney. The pulmonary vein passes along the edge of the cut 

 on the right side towards the auricle. It is joined, but this fact cannot be 

 seen here, before it enters the auricle by the efferent kidney veins. The 

 right border of the pulmonary chamber which is applied to the line of the 

 suture in the shell is relatively thick. It is muscular, and muscular fibres 

 pass off from it into the roof of the chamber. One of the vessels bringing 

 venous blood to the chamber runs along this border. 



When the animal is retracted into its shell by the action of the colu- 

 mella muscles, seen in the next preparation, air is forced out of the 

 pulmonary chamber ; conversely, when the animal expands again by the 

 contraction of the muscular integument including the floor of the pulmonary 

 chamber, air is drawn in But, except during the acts of expansion and 

 retraction, interchange of air in the pulmonary chamber with the air without 

 must take place only by diffusion. 



The foot is relatively large in most Pulmonata, and simple in contour. It is 

 divided by a transverse furrow into a fore- and hind-part only in Pedipes and Auri- 

 cula brunnea. The sole of the foot is ciliated, and in Arion its lateral walls as well. 

 A supra-pedal gland appears to be present in all Pulmonata, as well as in some 

 other Gastropoda (Azygobranchia, Opisthobranchia). It opens above the anterior 

 margin of the foot beneath the head. It consists of a ciliated duct extending back- 

 wards in the substance of the foot near its coelomic surface. Into this duct open 

 unicellular glands. Sense cells have been stated to be present in the epithelium of 

 the duct ; but it is very doubtful if the gland has the olfactory function which has 

 been ascribed to it. A caudal aggregation of mucous glands, situated posteriorly 

 on the dorsal aspect of the foot and opening into a depression of the integument, 

 is found in Arion ater and some other Slugs. But no Pulmonate possesses a pedal 

 gland opening near the centre of the creeping sole of the foot, such as is found in 

 many Azygobranchiate Gastropoda. A supra-pedal and a pedal gland coexist in the 

 Azygobranchiate Cydostoma elegans, which leads a terrestrial life. The aperture of 

 the pedal gland has often been taken for an aquiferous pore. 



Many Mollusca possess the power of suspending themselves by mucous 

 threads, and not only those of terrestrial habit but aquatic as well, e.g. Limneidae^ 

 and the marine Litiopa and Rissoa parva. In the Limacidae the thread appears to 

 be derived from the mucus coating the surface of the body. 



