116 M.A de Quatrefages on the Classification of the Annelides. 
upon a minute investigation of the nervous system in the Neretdes 
and allied genera*. 
What the 8 yllidea present which is very remarkable from the 
point of view here under consideration is, that in them the arma- 
ture usually belongs precisely to a portion of the trunk which 
is unarmed almost “everywhere else, and that the median portion, 
the essentially dentary portion in the best-armed Annelides, is, 
on the contrary, unarmed in them, with the exception of the few 
species indicated in my table. 
10. Moreover, and I have taken care to insist upon this con- 
sideration in my general remarks on the family Syllidea, my work 
relative to this group can only be regarded as provisional on 
many points. We have here a complete little special world, in 
which the variability of characters increases more than anywhere 
else, which appears to obey certain physiological laws which 
manifest themselves very rarely in the class, and always in very 
small species and in groups which are exceptional in other 
respects,—distinction of sexes, geneagenesis. I long for the 
moment when some naturalist will make a special study of this 
little world; and notwithstanding what M. Claparéde has lately 
written to me, I like to hope that he will fulfil this difficult task, 
for which no living naturalist appears to me so well qualified as 
the author of the ‘ Beobachtungen ’ and ‘ Glanures.’ 
11. [have still to reply toa serious observation of my learned 
critic. M.Claparéde thinks that I have retained with the same 
value all the genera the representatives of which have been for 
some years recognized as being only different forms of one and 
the same species. ‘The perusal of my book will absolve me on 
this pot. I have taken account of all the discoveries of this 
kind known to me, and especially of the work of A. Agassiz upon 
Autolytus; but I did not think it was yet time to come to a 
conclusion. We have here (at least in my opinion) an entire 
series of facts which science has only as yet touched upon, and 
which still require numerous and probably patient investiga- 
tion. I have my doubts as to some of the results announced 
with most certainty; but even if all that has been said upon 
this subject were correct, this all is still very little. It therefore 
appeared to me to be wiser to postpone conclusions which facts 
may contradict to-morrow; and I have accordingly, in general, 
left these genera among the incerte sedis and in the quality of 
mere indications, as several of them will no doubt have to dis- 
appear, while some will perhaps remain to science. 
12. But I have not, as M. Clapareéde thinks, gone so far as 
to place one form in one family, and another form of the same 
* “Mémoire sur le systeme nerveux des Annélides”’ (Ann, des Sci. Nat. 
3° sér, tome 1x.), 
