No. 4.] HIRUDINEEN STUDIEN. 2 I 5 



The cells nearest to the receptaculum are very large, possess 

 a large nucleus with loose linin network, very large nucleoli, 

 and loosely scattered chromatin granules. The membrane of 

 the nucleus is very thin. The shape of the latter is very 

 irregular, numerous processes projecting all over the surface. 



The cytoplasm appears as a beautiful clear network with 

 rather wide meshes. This network is not, as Bolsius states, 

 radially arranged, but it is equally well developed in every 

 direction. The microsomes cluster around the cytoplasmic 

 threads. 



These cells are filled with two kinds of vacuoles, some large 

 ones near the periphery and great masses of exceedingly small 

 ones near the center of the cell. 



In the cells farther away from the receptaculum the periph- 

 eral vacuoles have partly fused together, forming an irregular 

 network of canals, and the vacuoles of the central masses also 

 fuse more and more together and ultimately form one single 

 central canal in the cell. 



As soon as this central canal is definitively formed a new 

 group of structural elements becomes conspicuous in the cell, 

 namely, the peripheral organs. 



They appear at first only in the shape of microsomes, a trifle 

 larger than the other microsomes of the cell and more regularly 

 arranged along the inner edge of the cell surface. The farther 

 away we go from the receptaculum the larger these peripheral 

 microsomes grow and the more regularly they are arranged, 

 until they become finally eight to ten times as large as the 

 other microsomes and are each of them attached by means of 

 a thick, strongly staining cytoplasmic thread to the surface of 

 the cell. In the meantime the central canal becomes a wide 

 tube (in some cases bifurcating in places), and the network of 

 peripheral canals becomes united with the central canal, forming 

 elegantly ramifying side branches of the latter. 



The cells of the portio glandulosa-efferens next to these are 

 pierced only by the central canal, which shows no more bifurca- 

 tions and possesses no more side branches. 



The cells are smaller than those of the portio afferens-glan- 

 dulosa, as are also the nuclei, which are perfectly smooth and 



