204 W. BLAXLAND BENHAM. 
maturity is over (Pl. VI, fig. 32), as it shows very distinctly 
the shrunken sperm-sacs, the ovaries and testes. The sperma- 
thece are apparently undergoing degeneration ; they are filled 
with highly refracting globules. No trace of the sperm-duct 
or atrium, nor even penis was present; but in other speci- 
mens traces of the male apparatus could be detected. This 
disappearance of the penis appears to me particularly remark- 
able, though I am unable to say whether it is due to its solu- 
tion or absorption by the cells, or whether the hard coat is 
thrown off. 
Comparison of Heterocheta with other Tubificide. 
The nearest genus to Heterocheta is undoubtedly Psam- 
moryctes (Pl. VII, fig. 33), on which alone are found palmate 
cheetze closely resembling those of the former genus. In its 
generative apparatus, too, there is a pretty close agreement,! 
in the division of the atrium into two regions, and in the 
general form of the chitinous penial coat; but this is quite 
characteristic in Heterocheta. The chief differences 
between the two genera are (a) the restriction, in the latter 
genus, of the palmate chet to Segments v to x111, which in 
Psammoryctes commence in Segment mu and extend to x; 
and (4) the absence of capilliform chete in Heterocheta. 
As the various genera of aquatic Oliogocheta occur pretty 
abundantly in England, and as we have no brief summary of 
generic characters, I have brought together the chief charac- 
teristics in the form of a series of figures, and will point out 
here the leading features of these genera.” 
Commencing with the chete of the dorsal bundles—for 
those of the ventral are essentially similar in all the family 
except Telmatodrilus, we have a fairly ready means of dis- 
tinguishing groups of genera. 
1 T have not been able to see the dilatations in the atrial duct described by 
Vejdovsky. 
2 Stole, in a recent paper in the Czech language, adds considerably to our 
knowledge, so far as I can judge from the plates. 
