TJie Lungs, Heart, and Blood-vessels of the Slug. Ill 



till they reach the adjacent intestinal fold, and then separate. 

 One branch passes toward the head, running in its course 

 beneath the reproductive organs, heart and pericardial gland, 

 and parallel with the rectum, and finally becomes lost in sup- 

 plying branches to the gullet and organs of the head. The 

 other travels backwards toward the stomach, giving off about 

 twenty branches to the intestine and liver, the twigs to the 

 intestine being given off distinctly and passing over the hepatic 

 organ to their destination. These vessels divide and sub-divide 

 extensively, and form the most beautiful ramifications upon 

 the digestive canal, which they contrast with forcibly, being of 

 a snow-white colour, whilst the intestine owing to its vegetable 

 contents is usually green. On arriving at the stomach the main 

 artery bifurcates (divides in two), one branch passing backwards 

 to supply the egg-gland and tail-lobe of the liver ; the other 

 being destined for the stomach and left division of the liver, 

 upon whose inferior surface a series of very pretty arborescent 

 vessels may be observed. 



I believe that the view of Erdl,* that a network of capil- 

 laries exists, is erroneous. 



lstly. Because even the most careful scrutiny fails to detect 

 anything in the shape of capillaries. 



2ndly. Because the rootlets of the veins terminate undoubtedly 

 in apertures. 



3rdly. Because the whole of the organs in the hinder part 

 of the body are free, that is to say, unattached to the general 

 integument in which the veins lie ; and as the arterial supply 

 is almost exclusively to these organs, had there been any system 

 of canals intervening between them and the skin, the latter and 

 the viscera would be adherent to each other in this locality. 

 The arteries are composed of nucleated muscular fibres, which 

 embed in their substance a large quantity of carbonate of lime 

 (chalk) in the granular condition, which gives the vessels their 

 peculiar white colour. Professor Von Sieboldf asserts that the 

 ends of the arterial tubes are built up of chalk particles only, 

 without a trace of muscular fibre. I have been unable to confirm 

 this assertion ; in all the specimens which I examined (where it 

 was possible to form a conclusion) I most distinctly observed, 

 mingled with the granules, long nucleated endoplasts. 



The blood of the slug is colourless, but it is not as some 

 might imagine, a homogeneous fluid. It is composed of a 

 transparent liquid, consisting of water, a small quantity of 

 albumen, and a trace of fibrine. This fluid contains in it certain 

 bodies of a spherical form termed corpuscles, and these latter 



* De Helic'is Algiree. Bruxelles. 



f Vide " Vergleivhenden Anatomie." Section — Cephalophora . 



