NOTES ON SOME AQUATIC OLIGOCHATA. 205 
Telmatodrilus, Eisen, possesses only one kind of cheta, 
simple, unforked, sigmoid forms, resmbling those of En- 
chytreus. 
Limnodrilus and Clitellio likewise possess only one kind 
of chet (Pl. VII, fig. 35), namely, the furcate or “ crotchet,”’ 
which may vary in detail in different regions of the body.1 
In Hemitubifex, too, there is only one kind generally, 
though Eisen and Beddard mention capilliform chzetze as 
“sometimes ” occurring. I have not seen them in H. ater. 
Tubifex (fig. 34) and Ilyodrilus (fig. 33) present us with 
capilliform chetz, either only anteriorly in Segments 111 to x 
(or thereabouts) in the former, or throughout the body in the 
latter genus ; these chetz are confined to the dorsal bundles, 
and with them occur furcate chetz, which possess very 
usually two or more accessory prongs between the two main 
prongs in Tubifex,? or a membrane, without ridges or teeth, 
in Ilyodrilus. In both genera these modified furcate cheetz 
occur in anterior segments only. 
Further, in Spirosperma (fig. 36) capilliform chet occur 
all along the body, and are accompanied throughout by a pecu- 
liar variety of palmate chetz (see further on in this paper), 
which are small and inconspicuous.? They differ in shape 
and size from those of Heterocheta and Psammoryctes. 
Another set of characteristic modifications affects the male 
apparatus. 
The shape of the atrium, presence or absence of prostate, 
and penial coat are among these. The prostate is absent in 
Clitellio and Ilyodrilus. In the remainder it is a some- 
what kidney-shaped, solid mass of cells communicating with 
the atrium at the point of entrance of sperm-duct. 
1 Bothrioneuron, Stole, so far as cheetee are concerned, agrees with 
Limnodrilus. 
2 T have not seen the membrane between the forks, as figured by Professor 
Lankester. 
3 In Stole’s genus Lophocheta somewhat similar chetez occur in the 
dorsal bundles, together with peculiar feathered capilliform chete; but the 
exact distribution of these I am unable to give, as I have not yet had Stole’s 
paper translated. 
