344 Prof. E. Claparéde on the Structure of the Annelida. 
de Quatrefages. However, we shall see that, in certain cases, 
not only the buccal segment, but also some of the following 
segments receive their nerves from the cesophageal connectives, 
as in certain Aphroditea, some Hesionea, &c. According to the 
theory of M. de Quatrefages, it would be necessary to regard the 
whole of these segments as constituting a multiannular buccal 
segment ; and yet each of them bears a pair of feet, and other- 
wise presents all the characters of an independent segment. 
For my part I employ the name of antenne for all the appen- 
dages of the cephalic lobe; but where two of these appendages 
originate from the lower part of this lobe, at the same time 
acquiring special anatomical and physiological characters, I give 
them, like most other authors, the name of palpi. The modified 
cirri of the buccal segment and of the following segments are 
designated in this memoir as ¢entacular cirri. 
Without wishing to enter into details here upon the structure 
of the feet in the Annelida, I desire to indicate what are the 
relations of the sete to the tissues which surround them. 
Some authors regard them as enclosed in a sac which is only an 
invagination of the integuments; others think that they are 
formed in an internal follicle, and only secondarily arrive at the 
surface. This second opinion only is correct. In certain cases 
(in Hesione and others, for example) the whole bundle issues in 
a compact form through a single pedal aperture; but in others 
each seta has its own orifice. This is the case especially with 
the flabelliform bundles. The pore from which each seta issues 
is not previously formed, but is perforated by the seta itself. 
This is easy when the tissues of the worm are soft. But this is 
no longer the case when the Annelide is protected by a resistant 
cuticle, and when the seta, armed with hooks in various direc- 
tions, seems fit to get itself entangled in the tissues and to 
produce serious lesions in them. In these cases the extremity 
of the young seta is surmounted by a small provisional apparatus 
terminated by an extremely sharp plate, destined to cut a free 
passage for the seta in the tissues, and to prevent tearing. 
The form of this piece varies greatly, like that of the seta and, 
especially, that of the hooks, the passage of which is to be effected 
without lesion of the neighbouring parts. I have already pointed 
out some examples of this singular arrangement, but they have 
been passed over without notice. Many others will be found in 
the course of this memoir*. | 
Integuments and Muscular Apparatus. 
The integuments are composed of two layers :—one internal 
* See especially under the head of Aphrodita aculeata, where this sub- 
ject is treated in detail. 
