286 
A. G. BOURNE. 
walls of the central duct. This I have not found to be the 
case. 
Leydig Histologie des Menschen und der Thiere ’) added 
to previous knowledge of the general form of the nephridia 
of the Leeches (which was largely due to his own researches, 
especially that entitled Zur Anatomie von Piscicola,” 
^ Zeitsch. wiss. Zoologie,’ vol. i), an important fact of minute 
structure in which it is now known to agree with the ne- 
phridia of some other types, such as earthworm and larval 
Pulmonate Gastropods. He showed, in fact, by a figure to 
which there is no further allusion in the text, that the 
gland-cells of this organ are perforated by ducts, so that the 
cells have the form of hollow cylinders ; but he did not 
observe the more complicated condition of arborescent ducts 
discovered by Lankester, which I shall describe hereafter. 
The perforated cells figured by Leydig in his ^ Histologie ’ 
were from the nephridium of Haemopis. Claparede first 
showed that such was also the relation of duct and cell in the 
nephridium of the common earthworm (“ Histologie des 
Regenwurms,” ^ Zeitsch. wiss. Zool.,’ vol. 1869). 
Gegenbaur was the first to point out the complicated 
labyrinthine character of the ducts of the nephridium of the 
Leech when comparing that organ with the nephridium of 
the earthworm (^Zeitsch. wiss. Zooh, vol. iv), which he was 
the first to describe accurately. The condition of knowledge 
at the time when Gegenbaur’s observations w’ere pub- 
lished (five-and- twenty years ago) did not require a minute 
histological account of these organs, and, accordingly, w^e do 
not find histological details in his memoir. Excepting for 
the figure of cells from the nephridium of Heemopis, pub- 
lished by Leydig, there appears to have been no attempt to 
inquire further into the structure of this organ during later 
years; and we have the following account in Gegenbaur’s 
^ Elements of Comparative Anatomy ’(English edition, 1879), 
which may be taken as representing the actual state of 
knowledge wdth regard to them. It will be observed as an 
important point distinctive of the nephridia of the genus 
Hirudo that no internal opening has been observed leading 
from the body-cavity into the duct of the nephridium, and to 
the possible existence or non-existence of such an opening 
my observations have, inter alia, been carefully directed. 
Gegenbaur says (p. 176) : — ‘‘ So far as the structure of the 
excretory organs is concerned, few fresh characters appear in 
the Annulata (Hirudinea, Oligochseta, Chsetopoda). The 
organs correspond to the metamerism of the body, for they 
are regularly distributed on either side of almost every one 
