296 Introducti07i to Animal Morphology. 



In Pulmonates it lies between the pulmonary vein and the 

 heart ; in Prosobranchs between the gills and the heart, in 

 the floor of the gill cavity close to the beginning of the in- 

 testine. In Actaeon and Phyllirhoe it appears as a long clear 

 pouch ; a pair of similar pouches are present in the embryo 

 of Ancylus. Its outer opening in Prosobranchs is often duct- 

 like, usually has a sphincter, and often radial dilating fibres. 

 In Heteropods this organ contracts rhythmically, like a heart, 

 and is supposed to force water into the blood, and to act as a 

 portal heart, propelling the venous blood which it receives 

 into the heart. In Carinaria it has a lining of gland-cells, as 

 in Prosobranchs. In Opisthobranchs there are four types of 

 kidney: — ist, single, as in Prosobranchs (Phyllirhoe); 

 2nd, with its inner part differentiated as a portal heart, send- 

 ing blood into the pericardium and gills, the outer part re- 

 maining glandular (Fiona) ; 3rd, the portal heart developed, 

 while the renal part is obsolete (Janus) ; 4th, the outer 

 glandular part dissevered from the portal heart, which is often 

 absent (Doris). 



Other accessory glands are the purple glands in the wall 

 of the mantle in Dolabella, and over the whole surface in Aply- 

 sia, or beneath the intestine in the mesentery ; the depilatory 

 glands in Aplysia at the bottom of the right swimming 

 fold ; the foot gland in Slugs {Kleeherg) a cluster of unicel- 

 lular glands near the inner surface of the foot.* In Geoma- 

 lacus and Arion there is a similar tail gland. In Prosobranchs 

 transverse leaf-like mucous glands lie often on the roof of the 

 mantle cavity. In Fiona two large glands, whose function is 

 unknown, lie in the body cavity beneath the stomach, and 

 open under the mouth. Pleurobranchus tuberculatus has 

 surface glands at the base of its dorsal warts. 



The nervous system consists of a pharyngeal ring 

 with a pair of eyes, and a pair of hypo-pharyngeal 



* To get rid of the mucus in the dissection of Slugs and Snails, Gulliver 

 recommends drowning them under an inverted tumbler filled with water 

 and placed in a basin. For marine Molluscs the best method of pre;)ara- 

 tion is to kill the animal with vinegar, then to open its visceral cavity by a 

 long slit, and immerse for an hour in spirit of wine before dissecting. 



