NOTES ON ACANTHODRILOID EARTHWORMS. 299 
pores in an “abnormal” position than in the normal, i. e. 
in front of the ventral chete. The ‘ abnormal” position 
is itself variable, the pore sometimes occurring in front of the 
dorsal cheetz, sometimes dorsal of these, and even near the 
mid-dorsal line. Borelli does not state whether there is any 
approach to an “alternation,” or whether the variability is 
more marked posteriorly than anteriorly. 
There is little doubt that this sort of irregularity is of more 
frequent occurrence in other genera than we are apt to think. 
We have, amongst recorded cases (besides Plutellus), Beddard’s 
description of Acanthodrilus dissimilis! and Ac. rose,” 
&c., where the alternation is not regular; Bourne’s Perionyx 
saltans,® where there are two rows of nephridiopores, usually 
regularly alternating, though he mentions certain variations; 
Fletcher’st “Cupptodrilus” mediterreus, with an irre- 
gular alternation, and Megascolides tasmanicus, where 
the pores are in a sinuous series. 
The deviation from any fixed positions is especially interesting 
in these genera, such as Acanthodrilus, Megascolides, 
and Cryptodrilus, in which some species are in a plecto- 
nephric condition, for it seems to support the theory of Beddard 
and Baldwin Spencer that this condition is primitive, and that 
the network communicated with extensively many scattered 
pores, as in Pericheta, &c.; when the meganephric condition 
supervened, by aggregation and enlargement of some portion 
of the network, the pores enlarged, and the nephridia now 
opened, not at some fixed point, as has usually been presumed 
to be the case, but at any point on the surface of the seg- 
ment, the relatively fixed portions being probably a later 
phenomenon, and its relation to the bundles of chetz being 
due to some secondary causes, with which at present we are 
unacquainted, 
‘Proc. Zool. Soc.,’ 1885, p. 822. 
This Journal, vol. xxx, p. 434. 
‘Proc. Zool. Soc.,’ 1886. 
‘Proc. Linn. Soc.,’ N.S.W., 1887, p. 601. 
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