<?/■ Tetrastcmma graecense, Dohmig. 325 



network of canals, as well as into the finer one in the cephalic 

 regrion, there open numerous fine straiicht caualicules, upon 

 which lie the tertninal orfjaus, which are easily reco{j;tiizable 

 owincf to the active niovenionts of tiieir cilia-flames. Infor- 

 niation as to the fiiior structure of the excretory organs is 

 afforded by microscopical sections. In these may be observed 

 on each side, chiefly towards the dorsal surface and laterally 

 to the intestine, a raniifyins; cord of cells of varying size, 

 from which, however, isolated branches also pass over to the 

 ventral side. There is no communication at any point 

 between the two lateral cords of cells, although they some- 

 times approach so closely as almost to come into contact. 



For the sake of clearness it appears to me to be advan- 

 tageous from a descriptive point of view to distinguish three 

 sections in the excretory organs — namely, the end-canalicules, 

 upon which lie the terminal organs, the connecting canals, 

 and the main canals. 



'J'he first-mentioned lie for the most part close beneath the 

 dermo-muscular tube, and further on in immediate proximity 

 to the wall of the intestine ; their transverse diameter amounts 

 to about 3 to 5 /L6. Their wall consists of flat cells, which 

 take but a slight stain, and the respective limits of which can 

 only be made out with difiiculty. The cell-plasma is homo- 

 geneous in character or else finely granular, not infrequently 

 of greater density on the outer and inner surfaces, a fact to 

 which the somewhat greater stainability of these cells is 

 probably also to be ascribed. I never observed cilia or more 

 strongly developed single flagella in the case of these cells. 



The connecting canals which join the end-canalicules are 

 distinguished from the latter not only by greater thickness, 

 but also by the fact that tiie cells forming their boundaries 

 possess a cylindrical shape and a more strongly granular, not 

 infrequently finely vacuolate, protoplasm, which is capable ef 

 taking a more intense stain. These cells appear always to 

 bear cilia, though I have succeeded in recognizing the delicate 

 fringe of cilia only in certain preparations. 



Lastly, if we examine sections through the main portion of 

 the organ, we observe, in the first place, a complex of cells 

 which is traversed by canals in all directions. Closer study, 

 however, shows us that even here each canal has its own 

 cellular wall, but that the cells of the different canals often 

 lie extraordinarily close together, and that there are tracts 

 where the limits of the cells are not recognizable. These 

 cells vary considerably in size, but they are always larger 

 than those of the connecting portions. Their plasma is 

 granular and very frequently interspersed with a large number 

 of vacuoles; they, too, in life probably possess a clothing of 



