in the Oligochaeta. The botryoidal tissue of Hirudo has I can not doubt 

 precisely the same signification as the yellow- coloured tunic of the in- 

 testine and large vessels of Lumhricus. More especially I would com- 

 pare it to the coecal vascular processes covered with yellow granular 

 cells which project from the walls of the alimentary canal of Lumhri- 

 culus. 



I am inclined to think that both Le y dig and Brandt may be 

 right as to its function to a certain extent. Ley dig has already 

 pointed out that the liver in Paludina may have a function as a fatty 

 body — a store-house of combustible material. At the same time there 

 is evidence for the opinion that not only in Vertebrates but in Mollusca 

 also the cells of the liver are active in the production of colouring 

 matters'similar to Haemoglobin. Sor by has found such a colouring 

 matter in the stomach of Helix in the winter (Quart. Journ. 

 Microsc. Science. Vol. XVI. p. 78). Now though the yellow tunic of 

 the Chaetopods intestine and the brown botryoidal tissue of the Leech 

 are morphologically quite distinct from hepatic-cells, being products of 

 the mesoblast and not cells contained within diverticula of the enteron, 

 — yet in function these cells may have some analogies. The yellow 

 tunic and the botryoidal tissue certainly do not secrete any substance 

 which aids in digestion or which can directly reach the alimentary 

 cavity, but so far as their fatty nature is concerned they may represent 

 the hepatic cells and also, it seems very possible, they may be the seat 

 of the production of the haemoglobin which is diffused in the liquid of 

 the blood-vessels related to them. 



It is to be noted in comparing the yellow tunic of Chaetopods with 

 the brown botryoidal tissue of the Leech , that the cells of the former 

 are freely exposed to the body-cavity and separated from the closed 

 vascular system by the proper walls of the blood-vessels ; whilst in the 

 latter, in which there is no differentiation of closed vessels from body 

 cavity, the brown cells form the walls of fine channels containing 

 the haemoglobin-coloured fluid which is common to all spaces in the 

 Leech's body (excepting of course the alimentary canal) . 



Blood-vessels and blood-corpuscles. There is still 

 much to be made out with regard to the relationships between the 

 Leech's system of blood-spaces and the double system of body-cavity 

 and red vascular system obtaining in Chaetopods. It may be definitely 

 stated that^in the medicinal Leech there is no system of spaces occupied 

 by a colourless liquid. At the same time the large vessels with definite 

 muscular walls can be distinguished from the large sinus-like spaces, 

 and the small regular vessels with clear walls from shrunken vessels 

 with pigment granules (mentioned above as related to connective tissue 



