STUDIES ON EARTHWORMS. 247 
seem to have some sort of relation to one another, for in the 
Anteclitellian worms, where the clitellum commences some- 
where about xxv or further back, the gizzard is behind the 
genital organs. But in the Postclitelliani and Intraclitelliani 
the gizzard passes forwards to somites vi or vii, and is usually 
in the same somites with or in front of the seminal reservoirs. 
In the forms which have not a complete clitellum there is 
very frequently a glandular ridge on each side of the ventral 
surface, along or near the ventral edge of the clitellum. This 
is seen in Lumbricus, where Eisen (15) speaks of it as 
“tubercula pubertatis.” Perrier figures the same sort of ridge 
in Rhinodrilus, but whether it occurs in other forms I do 
not know. It very probably does so as it would appear to have 
some function in copulation. 
The true limits of the clitellum anteriorly and posteriorly 
are not always evident, as the thickening of the epidermis is 
gradual, and frequently is apparent on the dorsal surface before 
it is so ventrally. 
Dorsal Pore—In many Earthworms the celom is put into 
communication with the exterior by means of a series of 
“dorsal pores” placed on the intersegmental grooves. In 
Lumbricus these pores occur in every somite after about 
somite vir. In Digaster and Perionyx they commence 
just behind somite rv. In Plutellus behind somite vr. In 
Pleurochetaand Typheus the pores are present only behind 
the clitellum. They are present in Acanthodrilus, and in 
many Perichete. 
The Alimentary Tract.—The main regions into which 
the digestive canal is divided are constant in all the Earth- 
worms. There is a pharynx, cesophagus, gizzard (except in 
Pontodrilus), and an intestine. 
The pharynx is a strongly muscular organ and of glandular 
appearance, though in Lumbricus and others I can find no 
glands in the wall. Perrier has found glands in the pharynx of 
Pontodrilus. The anterior part of this organ has quite 
thin walls, and is in some at least capable of slight pro- 
trusion. This thin-walled region is the ‘ buccal” region, 
