156 THE ANNELIDES. §$ 146. 
With the Branchiati, these organs are often of a cultrate, lanceolate, 
or sagittate form. Often too, they are denticulated, or barbed upon one 
or both of their sides, and sometimes they appear articulated. These 
stings and bristles are moved by a special, muscular apparatus, consisting 
of many short muscles which arise from the internal surface of the cavity 
of the body and pass obliquely front and behind to the, bases of these 
organs. These bases project into the cavity of the body, and as their fas- 
ciculi aré surrounded by a common membranous sheath, when all the mus- 
cles contract at once, these organs are thrust out; but they move in va- 
rious ways, when the muscles contract separately. The other transverse 
muscles which pass either from the median line of the belly, or from the 
anterior and posterior parts of the body, and are inserted at the base of 
these organs, retract them anew into the cavity of the body.® 
2. With many Branchiati, there is a group of longitudinal muscles at 
the cephalic extremity, which, arising from the internal wall of the ante- 
rior segments, act as elevators and depressors of the oesophagus, as well 
as retractors and protractors of the fusciculi of the cephalic bristles and 
tentacles. 
CHAPTER III. 
NERVOUS SYSTEM. 
§ 146. 
The nervous system is highly developed in all the Annelides excepting 
the Nemertini. i 
The central is distinctly separated from the peripheric portion. The 
first is usually composed of a row of ganglia, joined together by nervous 
cords upon the median line of the body. 
The most anterior ganglion, and which in some. respects may be consid- 
ered analogous to the brain of the higher animals, rests upon the cesoph- 
agus, although the rest of the ganglionic chain which is situated on the 
median line under the digestive canal, may be regarded as a ventral cord. 
This cerebral ganglion differs from the others in its larger volume, and 
appears to be the product of a fusion of two or more symmetrically-arranged 
unequal-sized ganglia. These ventral ganglia are of uniform size, although 
not always of the same number with the segments of the body. 
Strictly, each of them is composed of two ganglia blended together either 
very perfectly, or very incompletely. The cerebral ganglion is joined to 
the first of the ventral chain by two cords which surround the cesophagus 
2 For the nearly inexhaustible variety of form 8 See Rathké, De, Bopyro et Nereide, p. 31, Tab. 
of these horny locomotive organs, which, whén II. fig. 7, 12; Grube, Zur Anat. d, Kiemenwiirmer 
cultrate, or lanceolate, are used as weapons of de- p. 5; and Q@ruithuisen, Anat. d. geztingelten 
fence, see dudouin and Milne Edwards, Olassifi- Naide, in the. Nov. Act. Acad. XI. p. 240, Tab. 
cation des Annélides, loc. cit. XX VII. p. 370, and XXXV. xe 
Orsted, Gréulands Annulata und Annulatorum 4 Aphrodite, Nereis, 
6 Ai 
t and Arenicola. 
Yanicorum Conspectus, fasc. I. Pl. I. phitrite, and Siph t d 
