STUDIES ON EARTHWORMS. 245 
This difference in the position of the nephridiopores helps to 
confirm Prof. Lankester’s theory as to the original presence of 
two pairs of nephridia in each somite, one series of which has 
disappeared in one set of worms, whilst the other series has 
gone in the second set, excepting in the genital somites, where 
they have been modified for the conveyance of the genital pro- 
ducts to the exterior. This is well seen in such forms as 
Eudrilus, where the nephridiopore is in line with the lateral 
couple, and the male pore in line with ventral couple. In 
Anteus no sperm duct is known, but the nephridia are some- 
what modified in the genital region, and may possibly serve as 
sperm ducts. It would be extremely important if it could be 
shown that such is really the case. 
The pores of the spermathece are always anteriorly placed 
except in Eudrilus, where they are behind the seminal 
reservoirs [and in Microcheta, where they are still further 
back], and are rarely placed laterally asin Pericheta affinis, 
but more often in a line with the ventral sete, as in Plu- 
tellus, Digaster, Pontodrilus, or as in Lumbricus,a 
little dorsad of these sete. In Pontodrilus they are in a 
line with the first seta, in Plutel]us they are in line with the 
second seta; again, in Urocheta they are in line with the 
lateral third seta. In Perionyx the pores are ventrad of the 
first seta. 
The pores are either on the anterior or on the posterior edge 
of the somites, so close to the edge that they appear to be on 
the inter-segmental groove. 
The Clitellum.—The clitellum has been taken by Perrier 
as the basis of his classification of the Terricolous Oligocheta, 
and it is only in a very few cases that it is absent. 
Moniligaster has certainly no clitellum, although its 
genital organs are described as being fully developed. 
Helodrilus and Criodrilus were described by Hoffmeister 
as having no clitellum, though sufficient details of the genital 
organs are not given by him, and the worms have not been 
studied recently. 
The various genera belonging to the four groups, Anteclitel- 
