268 RAMBLES OF A NATURALIST. 



we are apt to suppose, and often when two means 

 present themselves for attaining the same object, 

 she employs both at once. The arrangement to 

 which we have referred is to be met with in certain 

 Molluscs, of which some, at any rate, possess a heart. 

 Here, there are indeed no veins, but a more or less 

 complete arterial system conveys successively to all 

 the different parts of the body the liquid enclosed 

 in the general cavity ; nevertheless the stomach 

 sends forth prolongations to all the appendages, 

 including even the tentacles on the forepart of 

 the head, which, in the case of the snail, are im- 

 properly designated as horns. In obedience to the 

 simple laws of physics, the products of digestion 

 contained within these prolongations must neces- 

 sarily transude and mix with the liquid which fills the 

 body of the animal. These prolongations, therefore, 

 actually play the part of arteries by conveying 

 materials of nutrition to the points where they are 

 to be used. These same prolongations also fulfil 

 the functions of lacteals. The latter never convey 

 directly to the arteries the chyle which they have 

 collected from the surface of the intestine. In order 

 to render this liquid suitable to the maintenance of 

 the organism, it requires to be exposed to the modi- 

 fying action of the air in the lungs or branchias 

 which it reaches in association with the venous 

 blood. In the Molluscs to which we refer there 

 exist no branchiae which admit of a comparison with 

 those of other animals of the same class ; but here 

 their functions are performed by the small richly 

 coloured papillas which cover the bodies of these 



