288 
A. G. BOURNE. 
structure. After describing (this Journal^ 1879, p. 432) 
the segmental organs (nephridia) of the interesting Quatho- 
pod, Peripatus, as consisting of 1, a dilated vesicle ; 2, 
a coiled glandular tube ; 3, a short terminal portion, he pro- 
ceeds to say that though formed on a type of their own, the 
segmental organs of Peripatus more closely resembles those 
of the Leech than of any other form. The facts of the 
structure which I have to record as the result of my studies 
do not allow me to accept the view that there is any special 
similarity between the simple nephridium of Peripatus and 
the complicated one of Hirudo. The high differentiation of 
the nephridium of Hirudo appears in fact to have been 
overlooked by zoologists generally. 
II. — Methods of Investigation^ 
1. For the purpose of studying the nephridium entire and 
in the fresh state. Leeches were chloroformed and pinned 
in a gutta-percha trough, and opened by a dorsal median 
incision, the trough being filled with normal salt-solution. 
In this way any one of the series of seventeen pairs of 
nephridia could be dissected out whole and removed to a 
glass slide for observation under the microscope. 
The transparency of the organ renders this method of 
study of great value. ^ 
2. In order to obtain permanent and stained preparations, 
the nephridia, after excision, Avere placed in ^ per cent, 
osmic acid for tAventy minutes, Avashed in normal salt solu- 
tion or dilute alcohol and then stained for half-an-hour 
Avith Ranvier’s picrocarmin. Finally, they Avere mounted 
in glycerine. 
Other Avhole preparations of great value in the difficult 
task of folloAving out the course of the ducts and ductules, 
Avere obtained by placing Avhole nephridia in absolute 
alcohol, staining Avith hsematoxylin, clarifying Avith clove- 
oil and mounting in Canada balsam. 
3. Teazed preparations for the purpose of studying the 
minute characters of the tissues composing the organ were 
used. The nephridia Avere teazed either fresh, in salt solu- 
tion or in osmic acid, or after short maceration (tAventy 
minutes) in nitric acid (20 per cent, in Avater), or in Weiss- 
mann^s potash solution (40 parts caustic j)otash to 100 parts 
Avater),or after prolonged maceration (six months) in 2 per 
cent, aqueous solution of potassium bichromate. The latter 
method yielded valuable results, as also did maceration in 
-ptj per cent, chromic acid. 
4. The method of silver-staining Avas also applied to fresh 
