368 ALFRED GIBBS BOURNE. 
ing very pointed and is generally pink at the tip. The worms 
live in swamps and wet ground, hence no doubt the feeble 
thickening of the anterior septa (note in fig. 5 how the strong 
pharyngeal region is immediately followed in M. grandis by 
the four thickened septa). The intersegmental grooves are 
always most marked at the sides of the body, from about Seg- 
ment xiv onwards. The dorsal region often has a very smooth 
appearance ; the darker colour is, in spirit specimens (as noted 
by Benham), very sharply confined in this part of the body to 
this region ; papillz never protrude from the male pores. But 
when we come to diagnose species the matter becomes almost 
hopeless, and therefore most interesting. The trouble which I 
have had with this group is mainly responsible for the delay 
in the publication of this paper. I have at last determined to 
defer further examination of the matter till a future occasion. 
I have for the present made three species, and the diagnoses 
given above are the outcome of the examination of an enor- 
mous number of specimens, but the chances are about equal 
that any particular specimen which by external appearance I 
should refer to one of the three species, will or will not present 
an intermixture of characters. The three species are rather 
three types around which I can group the variations. 
In connection with these variations I have considered three 
factors,—age, habitat, and the production of hybrids. It is diffi- 
cult to altogether eliminate variations due to age. The condi- 
tion of the generative organs is of course the great criterion, 
but the transient nature of the clitellum introduces one diffi- 
culty, and I often find specimens in which some portion of the 
generative apparatus, particularly the ovisacs, has a very 
immature look while other parts are well developed. 
There is an undoubted tendency among worms to vary with 
even a slight difference of habitat (I have such variations re- 
corded for future publication in connection with a Perichete), 
but the variations partake in this case so markedly of an inter- 
mixture of the characters of the three types that they can, I 
think, only be explained by the fact that hybrids are produced, 
and although to make it certain the matter needs further 
