490 MR. F. E. BEDDARD ON THE 
forming therefore the innermost layer of the body wall, differs in no respect 
from the same structure in Lumbricus, 
Body Cavity. 
There is not very much to be said under this head. The body cavity com- 
municates with the exterior by a series of dorsal pores, one to each segment, com- 
mencing after the clitellum, and continuing to within eight segments of the end 
of the body; these dorsal pores are very general in the Oligochwta, and are found 
in Pericheta, Lumbricus, and other genera, but not in Pontodrilus and Urocheta.* 
Another fact of importance is the enormous thickening of some of the anterior 
mesenteries, which is not peculiar to Plewrocheta, but is found elsewhere. The 
last of these thick mesenteries separates the clitellum from the fore part of the 
body, and therefore marks the posterior boundary of the 12th segment, There 
appear to be six of these specially thickened mesenteries ; they extend forward 
to the posterior end of the gizzard, the first one marking the boundary between 
the 6th and 7th segments ; these mesenteries are united by ligamentous cords 
one to another, and as the “ hearts ” lie in this region of the body, their function 
may be to aid in their contraction, or perhaps they are merely protective. 
Similar thickened mesenteries are described by PERRIER as existing in Anteus 
and Urocheta ;+ and as Pleurocheta ought possibly to be regarded as one of the 
Intraclitellian Oligocheta, this fact may be of some significance. A transverse 
section through one of these thickened mesenteries shows that they are com- 
posed of two layers of muscular fibres. 
In the posterior region of the body the mesenteries are thin and mem- 
branous: in the most anterior segments the mesenteries are hardly at all 
separated, but are metamorphosed into a mass of muscles connecting the 
pharynx with the body wall (see Plate XXV. fig. 1). 
As has been already mentioned, there are no segmental organs in Pleuro- 
cheta; it is, however, not a unique example; in a Pericheta from Java, Dr. 
Horst{ asserts the absence of segmental organs, and generally throughout the 
genus Pericheta there is an absence or a very small development of these 
organs. 
Alimentary Tract. 
The alimentary canal of Plewrocheta resembles that of most other Oligo- 
heta in its main divisions. The mouth leads into a pharynx, the walls of 
* Perrier, loc. cit., p. 192. 
+ Perrier, Arch. de Zool. Exp., vol. iii. 
* Horst, “ Ueber eine neue Pericheta von Java,” Nederlandisch, Archiv. fiir Zoologie, iv. p. 163. 
