78 ANNELIDES. 



a Proboscis, viz, the oesophagus, or upper portion of the intestinal 

 canal, in a state of protrusion. It consists of one or two segments, 

 and is evolved at pleasure by a process of evagiuation. It is often 

 armed with horny jaws in opposite pairs ; sometimes roughened on 

 the surface with horny prickles ; sometimes villose with soft papillae ; 

 sometimes encircled at the orifice with soft papillae or short tentacles ; 

 and sometimes plain. These modifications of the organ afford im- 

 portant characters in classification. 



The Thoracic Segments immediately succeed the cephalic or head. 

 In the cephalous genera there is only one thoracic segment (fig.S^A) ; 

 as is also the case in many of the subcephalous. From its position, 

 I usually describe it as the post-occipital, — a name to be preferred 

 as implying no theory. It is remarkable for being naked, — that is, 

 it has no soft appendages or setigerous feet, and constitutes, some- 

 times, a sort of neck. 



In the acephalous genera, and less markedly in some others, the 

 thoracic segments are distinguished by peculiarities in their structure 

 and appendages ; — they are more fleshy and contain the primary 

 organs of life ; and to them the Branchise (fig. 10 6) are limited in 

 many genera. They are readily enough defined. 



The Abdominal Segments follow the thoracic and complete the 

 body. They are more numerous than the cephalic and thoracic 

 combined, more uniformly alike in their appendages, and liable to 

 vary in their number, so that, as a character, number is here of no 

 value, excepting in a few instances. They gradually lessen in size as 

 they approach the posterior extremity ; and the last segment is called 

 the anal. This has no setigerous feet, often no soft appendages, but 

 more commonly a pair of soft filaments, called styles, project behind ; 

 or a series of short papillae surround the vent, which is terminal and 

 central. 



The Segments are furnished with various appendages, which are 

 precisely similar on each side, but modified more or less on different 

 segments. Of these appendages the Foot is the principal, and with 

 it the others are commonly combined. 



The Foot is a papillary projection on the side of the segment for 

 the insertion of the bristles. It also affords, in most worms, a basis 

 of attachment to the Branchiae, and certain soft setaceous filaments 

 called Cirri or tentacular cirri. 



The Branchi^ are the breathing organs. In the cephalous and 

 subcephalous families they are attached to the base of the foot on 

 the upper or dorsal side, either restricted to a certain number of seg- 

 ments, or found on all of them. They vary much in form. They 

 are either arbuscular, or semipectinate, or flat and veined, when 

 their function is indisputable ; or they are filamentary, or squamous, 

 or lobe-like, or merely tubercular, when the ascription of the function 

 becomes arbitrary, or a deduction from the theory of homologies and 

 degradation of organism. In many acephalous genera the Branchiae 

 are placed on the crown in beautiful tufts (fig. 10) ; and in all 

 acephalous worms the function of the orga^^s is never doubtful. 

 They often combine a tactile with the respiratory office. 



The Cirri are the tentacula of the body ; and we may call them, 



