298 



(lulated with picric-acid did not produce better results and being 

 more troublesome was soon abandoned. 



Figiire 1 represents a dorso-ventral section of Hirudo medici- 

 ualis , which gives a fair idea of the topograpliy of the different 

 organs. 



The section is taken just perpendicular to that of fig. 2 and 

 a coutinuation of the two somewhat elucidates the structure of 

 the jaw. 



Ray Lankester has demonstrated the particular structure of the 

 integument of Hirudo and says, that the epithelium is built of 

 long mallet-like cells without nuclei. The cells are not placed 

 closely against one another , but leave everywhere a little space 

 between them , through which a well developed net of blood ca- 

 pillaries spreads its branches. 



This description is not quite right. The epithelium cells are 

 arranged one against the other and only here and there some 

 holes are left for the capillaries; only some cells have a mallet- 

 like shape. In my preparations there is a nucleus in each cell, 

 which stains very well with Haematoxyline. 



Bourne gives a good illustration of the epithelium ; the cells 

 lay close to each other and have distinct nuclei. The presence 

 of bloodvessels in the epithelium makes the skin an important 

 respiration organ. Gratiolet and others , who have studied the 

 complicate bloodvessels of the worms , knew these skin capillaries 

 and their function. 



On the surface of these cells the cuticula forms a thin trans- 

 parent homogeneous membrane, which envelops the whole body. 



The pharynx and the oesophagus are likewise lined by a high 

 epithelium but they are destitute of capillaries. 



ünder the epithelium of the skin glandcells are found, which 

 open with shorter or longer secretory ducts on the surface of 

 the body and are filled with granules. On the wall of the pha- 

 rynx these epidermicglands are replaced by glands with very long 

 ducts and with a contents of very small granules, much smaller 

 than those of the epidermicglands. These glands are known as 



