Prof. E. Claparéde on the Structure of the Annelida, 343 
A second inconvenience of the nomenclature of M. de Quatre- 
fages is that it is inapplicable in all those cases in which the 
anterior segments are much condensed, and in which it is no 
longer possible to determine to what segment a given pair of 
appendages belongs. We shall see, for example, that in the 
Phyllodocea and the Hesionea authors are unable to agree upon 
this determination, and that M. de Quatrefages allows himself 
to be led away by his theory of the appendages to establish 
genera which no one will adopt. We also find the learned 
Academician, for love of his theory, suppressing by a stroke of 
his pen the buccal segment in most of the Sigalionida, or at 
least attributing to them “an indistinct buccal segment, desti- 
tute of appendages.” But nothing is more distinct than the 
buccal segment of these Annelida; only it bears a pair of feet 
with sete, which a buccal segment ought never to do, ac- 
cording to the theory of M. de Quatrefages. Unfortunately the 
author does not suspect that all the Polynoe likewise bear some 
sete on the segment which he regards as the buccal ring, and 
_ that it would consequently be necessary to imagine in them an 
“indistinct buccal segment without appendages.” 
M. de Quatrefages, however, gives us a rule (difficult of appli- 
cation indeed, but still a rule) for the determination of the seg- 
ments and their appendages. The cephalic lobe and the an- 
tennz, he says, receive their nerves from the cerebral ganglion, . 
the buccal segment and its tentacles from the cesophageal con- 
nectives, and the tentacular cirri from the ventral ganglionic 
chain, ‘This thesis is not tenable in presence of the modern 
progress of embryology. Schaum asserted that in all Arti- 
culata a segment is characterized by the presence of a ganglion, 
and he started from this principle in denying that the head 
in Arthropoda is formed of several segments amalgamated to- 
gether. This doctrine was immediately refuted. In fact, the 
nervous system is comparatively very late in being differentiated 
in the embryos of Articulata; on the contrary, the appearance 
of the segments (the protozonites as they have been called) is in 
many cases the result of one of the first modifications of the 
blastoderm. These primitive segments unite in groups, and 
sometimes become soldered together, long before the differentia- 
tion of the nervous system; and when this system is developed, 
the number of its ganglia is not necessarily identical with that 
of the primitive segments. In the Annelida especially, the 
formation of the nervous system certainly sometimes follows 
very closely upon that of the segments, as in the embryos of 
Capitellus, for example; but most frequently it is much later. 
I do not, indeed, dispute that in many Annelida the origin and 
distribution of the nerves is in accordance with the rule of M. 
