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- 

 «iculi are 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 fasciculi of the cephalic bristles and 

 tentacles. '*' 



CHAPTER III 



NERVOUS SYSTEM. 



§ 146. 



The nervous system is highly developed in all the Annelides excepting 

 the Nemertini. 



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 oesoph- 

 .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 

 «necjual-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 oesophagus 



2 for the nearly inexhaustible variety of form 3 See Rnthki, De Bopyro et Nereide, p. 31, Tab. 



rof these horny locomotive organs, which, when II. flfj. 7, 12 ; Grube, Zur Anat. d. Kiemenwiirmer 



•cultrate, or lanceolate, are used as weapons of de- p. 5 ; and Gruithuisen, Anat. d. gezunjielten 



.fence, gee Audoiiin and Milne. Edioardu, Classifi- Naide, in the Nov. Act. Acad. XI. p. 2-10, Tab. 



nation des Ann61iiles, loc: cit. XXVII. p. 370, and XXXV. 



lÖmtF.d, Wriiiilands Annulata und Anuulatorura ■» Aphrodite, Nereu, and Arenicola. 



''>aQicorum Conspectus, fasc. I. PI. I. 6 Amphitrite, and Siphonostomum. 



