502 MR. F. E. BEDDARD ON THE 
by a layer of the peritoneum. No ducts were visible in communication with 
either of these pairs of orifices in either specimen. 
The sucker-like structure is possibly used by the animal during copula- 
tion. 
The two openings in the 15th segment, which were only visible in one of 
the two specimens at my disposal, had again no apparent duct connected with 
them. 
The clitellum of Plewrocheta is remarkable for being composed of an 
unusually large number of segments; in Perichwta the number is almost 
constantly three ; m Pontodrilus there are five, and in Urocheta hystrix as 
many as seven segments in the clitellum ; but Iam unable to recall any form 
except Pleurocheta in which there are more than this. 
PERRIER,” in an important memoir which has been already several times 
spoken of, divided the Oligochwta into three groups, according to the position 
of the male generative orifices. 
(1) The Antechtellians, e.g., Lumbricus. 
(2) The Lntraclitellians, e.g., Urocheta. 
(3) The Postchtellians, e.g., Pericheta. 
On PERRIER’S system the genus Pleurocheta would be regarded as one 
of the Intraclitellians, the generative openings lying within the clitellum; if, 
however, the apertures in the 17th and 19th segments in reality are connected 
with the testes, which unfortunately I have been unable to prove, then their 
position is somewhat intermediate between the Intra- and Postclitellians ; 
whether this be so or not, the number and distribution of the generative orifices 
in Pleurocheta are so peculiar and so different to anything known in the 
Oligocheta, that PERRIER’s system would be very artificial, if it proposed to 
unite in one family two such very divergent types as Urochwta and Pleurocheta. 
In many characters Pleurocheta resembles Perichwta, which is one of the Post- 
clitellian group; for instance, in the absence of segmental organs, in the 
presence of a pair of “ prostate” glands, and in the fact that the ovaries are 
small and difficult to find (I have not satisfied myself as to their existence in 
Pleurocheta) ; the last two characters distinguish the Postclitellians as a group. 
On the other hand, the presence of two ceca on the alimentary canal, and the 
double spermathecze, are invariably characteristic of Perichwta; these are 
absent from Plewrocheta. 
The characters in which Pleurocheta agrees with the Intraclitellians are, 
firstly, the position of the generative openings (?); secondly, the possession of 
only one pair of testes, which is a character found also in Urochwta and 
Titanus, and remarked as of importance for classificatory purposes by PERRIER, 
though it is not universal in the Intraclitellians. The thickening of the 
* Perripr, Nouvelles Archives, &c. 
