108 M.A. de Quatrefages on the Classification of the Annelies. 
said of reciprocal terms will perhaps some day explain some of 
the facts upon which the Genevese philosopher depends for the 
support of his opinion. Perhaps, also, in other groups than 
those with which we have to do here, we must definitively 
admit that the union or separation of the sexes has really no 
ereat importance with regard to affinities. 
But the value of characters is very far from being constantly 
the same in the animal series, as I have already remarked ; and in 
this case the moncecious or dicecious character appears to me to 
be in relation to so many other facts, that it seems impossible 
not to give it great weight. We do not yet, I believe, know any 
Erythreematous worm with the sexes separate; and only three 
exceptions to the diceciousness of the Annelides have been indi- 
cated: these three exceptions have been observed in groups 
which are still very imperfectly known, and which every consi- 
deration leads me to regard as exceptional in many other rc- 
spects. In a group with so variable a type as that of the Anne- 
lides, to find variations even in the characters of the class is far 
less extraordinary than elsewhere. But none the less does this 
fact appear to me more important than that presented by the 
species of Phoronis (Crepina, Van Ben.). These, which M. 
Claparéde regards as further removed from the Annelides than 
the Erythremata in general, are, in my eyes, evidently only 
Sabellea—very degraded, no doubt, but in which the general 
type of the Annelides is recognized at the first glance ; and this 
M. Van Beneden has not failed to perceive. 
The discovery of the segmental organ (Williams) in the Anne- 
lides has certainly established an additional relation between 
them and the Erythremata. But I do not know how far the 
presence of this organ is constant in the former of the two classes. 
Ehlers and Claparéde have found it in Sy/lis; but their descrip- 
tions, always very succinct and often not very complete, and their 
figures, which leave scarcely less to be desired, although adding 
to what the English savant has taught us on this subject, still 
leave room, it seems to me, for well-grounded doubts. In any 
case it appears from them that this apparatus in the Annelides 
has neither the development nor the constancy which it presents 
in the Erythremata. 
On the other hand, no Annelide possesses a ¢yphlosolis; and 
although I found upon the anterior vascular trunks of certain 
Arenicole (and in the Arenicole alone) something resembling 
the chloragogena, I was at the same time able to prove that in 
this case there was only a similitude of aspect. 
* In the introduction to my book I have only mentioned the fact disco- 
vered by Huxley. The observations of Pagenstecher had escaped me, and 
M. Claparéde had not yet discovered his Amphiglene. 
