344 Prof. E. Claparede on the Struct U7'e 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 oesophageal 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 multianuular 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 antennce 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 tentacular 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 setse 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 

 tei'minated 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. 



