<OLIGOCHATA OF TROPICAL EASTERN AFRICA. 259 
of this genus there isa single calciferous gland or rarely a pair of 
these glandsin the 9th segment ventral in position. The genus 
Gordiodrilus is mainly an African genus; it has been found 
in West Africa, and I describe in the present paper a species 
from Zanzibar. Gordiodrilus has no marked affinities to the 
Eudrilidz, and for the present I place it in that unsatisfactory 
family the Cryptodrilide. The only point of resemblance to 
the Eudrilide is in the median and unpaired calciferous gland. 
This gland is a diverticulum of the csophagus, which is sur- 
rounded by a mass of tissue exactly like that which makes up 
the greater part of the glands in Stuhlmannia and Eudri- 
loides. The cesophageal diverticulum, however, passes from 
end to end of the gland, and expands at its blind extremity into 
a network of fine tubes having an intra-cellular lumen and 
bearing the strongest possible likeness to nephridial tubes. This 
genus is noteworthy from the present point of view as furnish- 
ing an intermediate condition between the calciferous glands of 
the more typical earthworms and those of the genera Stuhl- 
mannia, Notykus, and Eudriloides. The lumen con- 
nected with the csophagus is reduced in extent and is not 
folded, while at the same time the peritoneal covering is greatly 
increased in importance. The next stage is furnished by 
Notykus. Stuhlmannia seems to me to have a still more 
reduced cesophageal diverticulum. Finally, in Eudriloides 
I could not detect any diverticulum at all. In this species the 
walls of the esophagus were much folded, so that a short diver- 
ticulum, if it exists, would be less conspicuous than in Stuhl- 
mannia. As the extent of the epithelial diverticulum of the 
cesophagus is lessened there is a corresponding increase in the 
amount and also in the specialisation of the peritoneum-like 
tissue which surrounds it. Already in Stuhlmannia there 
is a commencing conversion of some of these cells into a 
definite layer bordering the blood-vessels in certain regions. 
In Eudriloides the amount of this specialised tissue is 
increased and the specialisation has gone further.. It appears 
to me that this remarkable change in the histological characters 
of glands, which I cannot but consider to be the homologues 
