CONTRIBDTIONS TO THE ANATOMY OF THE HIEUDINEA. 481 



cells become ; it also shows the relation of the nephridial net- 

 work to the capillary network. By macerating a whole fresh 

 Pontobdella in nitric acid (10 per cent.), after cutting it 

 open and clearing away the alimentary canal, I have been 

 enabled to remove from the outside, first, the epidermis and 

 then, the muscular layers. By proceeding in this manner 

 with exceeding care, taking the muscles away a few cells at a 

 time, the nephridial network, extending over two or three 

 segments, may be left in a thin layer, containing, in addition, 

 the capillaries and gland-cells and connective tissue, and a few 

 muscle-fibres helping to hold it together. By such prepara- 

 tions, which at times are very successful, I have been enabled 

 to construct the diagrammatic drawing in fig. 8. 



Apertures to the Exterior. — At regular intervals, as 

 shown in fig. 3, the tubules collect together : the lumina be- 

 come much larger, and then communicate with a duct leading 

 to the exterior (fig. 65, we/jA. apert). This duct is lined by 

 numerous small cells, resembling ordinary epidermic cells, and 

 has the appearance of being invaginated from the exterior; it 

 is, indeed, lined by a cuticle. There is no vesicle or dilatation 

 corresponding to the vesicle of other genera (fig. G5). 



These paired apertures are situated upon the anterior and 

 outer surface of the second papilla (counting from the median 

 ventral line) of the first annulus in the ten segments, 10 to 

 19 inclusive (fig. 3). 



Branchellion. 



I have not had sufficient suitable material to be able 

 to speak with absolute certainty regarding Branchel- 

 lion. In one instance I obtained a living specimen small 

 enough to enable me, by very gradually increasing compres- 

 sion, such as adopted by Fraipont and Lang, in examining 

 the nephridia in Cestodes, Trematodes, and Planarians, to 

 observe the nephridial network. It is a perfectly continuous 

 network, occupying the same region of the body as in Pon- 

 tobdella, ; the tubules present a similar structure, but in this 

 young specimen, at any rate, I could only detect a single pair of 



