ANATOMY AND HISTOLOGY OF PLEUROCHATA MOSELEYI. 483 
gizzard, small and large intestines ; the large intestine is characterised by an 
extraordinary development of specialised glands. Certain of the anterior 
mesenteries are thickened and muscular; dorsal pores are very distinct, com- 
mencing after the clitellum, and extending to within eight or nine segments of the 
end of the body. No segmental organs were detected. Vascular system con- 
sists of a dorsal trunk, a ventral supra-nervian trunk, two small supra-intestinal 
trunks and two lateral ; the dorsal and ventral vessels are united by six pairs of 
arches, which increase in size from before backwards, the last two pairs being 
the thickest. The other vessels are not directly united, but indirectly by means 
of capillaries. The generative system consists of one pair of testes, which have 
the form of racemose glands, and are situated in the 12th segment; of two 
receptacula seminis opening respectively between the 7th and 8th, and 8th and 
9th segments ; of four fimbriated organs, with ciliated openings into body cavity, 
and duct opening to exterior through body wall of segment behind; these 
organs, concerning the nature of which it is difficult to speak with certainty, are 
situated in 11th and 10th segments on anterior wall of mesentery. A pair of 
rosette-shaped glands are found on mesentery separating 11th from 10th segment, 
the nature of which again is doubtful. In the 17th, 18th, and 19th segments 
are three pairs of openings, the middlepair of which are continuous with the 
ducts of two large solid white glands ; with the other two pairs of openings, no 
ducts were seen to be continuous. The clitellum extends from 13th segment 
to about 20th inclusive, and is readily distinguished from rest of body by its 
yellow glandular appearance ; another pair of openings, to which Professor 
MosELeEy drew my attention, are situated in the 13th segment. 
These are the main facts in the anatomy of Plewrocheta. I will now proceed 
to consider them in detail, and in so doing shall adopt the order in which 
M. Perrier, in his numerous and valuable memoirs on the anatomy of 
Oligocheta published in the Archives de Zoologie Expérimentale and other 
journals, describes the various organs and systems, for the purposes of an 
easier comparison. 
Tegumentary System. 
Under this head will be described the five layers which separate the body 
cavity of the animal from the external medium, commencing from the outside. 
(1) Cuticle—There is nothing particular to be said concerning its structure ; 
it appears to resemble in every detail the same structure in other worms, exhi- 
biting fine striz running in two directions nearly at right angles to each other, 
and minute pores situated frequently at the intersection of two strie. 
(2) Hypodernis.—The cellular layer which underlies the cuticle is generally 
described by this name ; concerning its structure in Plewrocheta I am not able 
