89 



fibre) and the moniliform brown vessels constituting the botryoidal 

 tissue. In the small vessels with irregular walls I have observed minute 

 pale corpuscles sometimes aggregated in quantity — but I have not 

 seen them in the clear walled vessels. 



The exceedingly fine capillaries which take a horizontal course 

 among the epidermic cells (noted above) furnish an example of the 

 completeness of the Leech's vascular system: this is still further 

 exemplified in the very complete set of minute capillaries which are 

 distributed to the nephridia in such a way that each constituent cell of 

 the gland is encircled by at least one loop of the vascular network and 

 in section may be seen to have as many as five separate capillaries 

 interposed between it and neighbouring gland-cells. In the comple- 

 teness of its vascular supply the nephridiura of the Leech strongly 

 recalls the similarly complete vascular supply of the Mammalian liver. 



The nephridia or excretory glands (Schleifencanäle) . 

 L e y d i g has figured a bit of the nephridium of Haemopis , showing 

 the large cells of which it is composed, each cell being actually perfo- 

 rated or traversed by the duct. Claparède has figured the same 

 structure for the nephridium of the Earthworm. The actual disposition 

 of the perforated cells in the nephridium of the medicinal Leech and 

 the mode in which they are set together so as to form a solid gland has 

 never been described. It is impossible without figures to give an idea 

 of the true relations of the lobes of the nephridium which has been 

 carefully worked out by my assistant Mr. A. G. Bourne. In the 

 apical region of the gland the cells are not perforated through and 

 through by the duct, but the duct has a finely arborescent origin in each 

 cell ; in another part the cells are perforated through and through by a 

 branching duct which joins the branching ducts which perforate neigh- 

 bouring cells ; again in the basal region of the gland the ducts become 

 very large and simply traverse successive gland-cells which are little more 

 than hollow cylinders. Everywhere the duct has a fine cuticular lining 

 which resists maceration and can be isolated. In addition to the tra- 

 versing or intra-cellular ducts , the lobes of the nephridium present 

 each a large axial or inter-cellular duct. The wall of the nephridial 

 vesicle or bladder is finely ciliated. The bladder contains a number of 

 excessively fine needle like particles — not merely granules as stated 

 byLeuckart. Micro-chemical examination renders it probable that 

 these needles are of a nature allied to that of the Uric acid. 



Silver-staining or maceration in Müll er 's serve to render appa- 

 rent in the nephridial gland-cells a very remarkable 

 fibrillar structure. After long maceration the cells will break up 

 into a number of exceedingly delicate rods — which are all set so as 



