M. A. de Quatrefages on the Classification of the Annelides. 109 
Again, as far as I know, we never find in an Erythreematous 
worm the foot, which is so characteristic of the Annelides. Their 
setee indeed resemble those of certain Sedentaria; they are 
set in motion by an analogous mechanism, and they are deve- 
loped nearly in the same way. But here the resemblance ends. 
The foot, as a well-marked and distinct organ, never makes its 
appearance. 
No Erythrematous worm has ever presented true branchiz 
comparable, even distantly, with those presented by so many 
Annelides. 
If we compare the nervous system of the Lwmbrict with that 
of the Annelides, selecting species in which it is at once most 
developed and best known, we ascertain considerable typical 
differences in the stomatogastric portion of these apparatus. As 
to the ventral chain, it cannot but present much similarity in 
Annulosa which continue faithful to the general type. 
To tell the truth, I can only find the vascular apparatus which 
can be seriously adduced in support of the proposed approxima- 
tion, although, indeed, there must be some resemblances between 
the two groups, as otherwise no one would have dreamed of 
confounding them. 
Thus we have genuine resemblances upon some points and 
profound differences upon others; and this, in sum, is what is 
presented by the Annelides and the Erythraemata when we take 
as terms of comparison their highest and most perfect represen- 
tatives. This apparent contradiction seems to me to be a 
general and decisive argument in favour of my opinion, which 
may be summed as follows :—the differences between the two 
groups depend on a want of real affinities; the resemblances 
spring from analogies; the class of Erythraemata and that of An- 
nelida are the corresponding terms or analogues of each other in 
two distinct series. 
That these two groups approach still more closely by some 
inferior derivative types, by some degraded species, I am far from 
denying. But do we not observe this even among the Verte- 
brata ? 
So much for the Erythremata. But M.Claparéde goes further, 
and would have the Hirudinea also placed in the class of Anne- 
lides. He is not the only person, as is well known, who holds 
this opimion. But in this case my opinion seems to me to be 
still more easy to defend. I shall only remind the reader that the 
resemblances existing between the Annelides and the Erythre- 
mata, as regards the vascular and nervous apparatus, disappear 
when we come to the Leeches. Nothing in the Annelides answers 
to the great lateral trunks of the latter; and the stomatogastric 
nervous system of the Leeches resembles that of the Insects rather 
