560 LECTURE xxn. 



the respiratory organs are indicated by the characters of the orders 

 already defined. In the terrestrial Gastropods the breathing organ 

 has the form of the simple undivided vascular sac {fig' 207. m ii) like 

 the lung in the lowest air-breathing Vertebrate animals : its orifice 

 m, is on the right side near the head. The forms of the aquatic 

 breathing organ are as various as is its position. 



In most of the Nudibranchiate species the gills are tufted and rami- 

 fied, as in the higher Anellides; they are penniform in the Haliotis, and 

 pectinated in all the dioecious Gastropods {fig. 204. g), as the name 

 of their order indicates : in these they never exceed two in number, 

 which are of unequal size, and the branchial chamber is usually pro- 

 longed into a siphon. In a few genera of amphibious Gastropods a 

 pulmonary sac is combined with branchial organs. The branchial 

 surface is ciliated in all the Gastropods, as is also the exterior surface 

 of the body in the small fresh-water species. 



As a compensation for the absence of gills, some Apneusta {Actaeon, 

 e. g.), have an aquiferous system, consisting of a reservoir, filled with 

 water, behind the heart, from which branched canals pass ofi" in all 

 directions, one of which, according to Vogt, opens on the right side 

 behind the vent. Conspicuous aquiferous pores are situated at the 

 centre of the foot, in CyprcEa, Conns, and Ancillaria, and at its mar- 

 gin in HaliotiSy Doris, and Aplysia. Delia Chiaje * has described 

 a similar system in many of the higher organised Gastropods. 



Besides the large and well developed hepatic and 'salivary glands 

 which are associated with the alimentary canal, we have seen that cer- 

 tain fucivorous Gastropods present the simplest rudimental condition 

 of the pancreas. The situation of the follicular urinary gland and of 

 its excretory duct has already been pointed out in the Paludina 

 vivipara: in some species the duct dilates to form a small recep- 

 tacle-t A group of follicular glands, sometimes imbedded in a distinct 

 glandular sac, is present in many species for the elimination of some 

 peculiar and characteristic colour ; the yellow liquid of the BuHcb, 

 and the famous purple secretion of the Purpura, are products of 

 saccular modifications of this follicular gland, which is situated 

 between the heart and liver. Numerous simple and scattered folli- 

 cular glands lubricate the mantle with its characteristic mucus in all 

 the Gastropods. In several terrestrial species, the median line of the 

 foot is occupied by a straight canal, lined with ciliated epithelium, 

 which ends in a large orifice beneath the mouth. On each side of 

 this canal are rows of follicles which secret a granular mucus.J A 

 follicle excreting a similar mucus opens on the extremity of each 



* CCCLXXIII. t CCCLX, p. 13. and CCCLXI. J XXIV. p. 343. 



