^§ 147, 148. THE ANNELIDES. 157 



laterally, thus forming a ring (the oesophageal ring) through which the 

 oesophagus passes. 



§147. 



The histological elements of the nervous system of these anii lals, are 

 arranged in the following manner : *^' 



The central mass of the nervous system is enveloped by a fibrous tissue 

 {Neurilemma), of longitudinal and transverse fibres which are often covered 

 with special pigment cells. 



The nervous cords and filaments are composed of extremely fine, primi- 

 tive fibres, between which in the ganglia are situated various-sized cell-like 

 ganglionic globules.^-' Some of these primitive fibres pass from the cere- 

 bral ganglion through all the ventral ganglia, while others pass off 

 from the central ganglia to the peripheric nerves. Many of the ganglionic 

 globules of the brain and abdominal cord are remarkable for their longer 

 or shorter prolongations which may be traced even into the roots of the 

 nerves. '■'' 



§ 148. 



The nerves are given off usually from the ganglia, and rarely from the 

 interganglionic cord. The cerebral ganglion sends off nerves to the organs 

 of sense in the head, and to the labial, proboscideal, and masticatory organs 

 about the mouth. Its development therefore corresponds exactly to the 

 more or less complicated condition of the cephalic extremity. 



The ventral ganglia send off from each side usually two or three sym- 

 metrically-arranged main nerves to the muscles and skin. 



It is with the Annelides that there have been found the first traces of a. 

 vegetative or splanchnic nerve {Nervus splanch?iicus) . This consists of deli- 

 cate filaments which are distributed upon the intestinal canal, with here and 

 there enlargements, and which anastomose, some directly with the oesophageal 



1 Our knowledge of the intimate structure of the and ventral ganglia of the leech so regular and 

 nervous system of the Annelides is as yet based symmetrical an arrangement of the ganglionic 

 upon researches of that of the Hirudinei only ; see globules, that those of the two lateral halve» cor- 

 Helmholtz, De fabrica systematis nervosi werte- responded exactly as to number, volume anc? posi- 

 bratorum dissertatio. Berol. 1842, p. 12 ; Hanno- tion ; see P'alentin, loc. cit. p. 208, Tab. VIII. fig. 

 ver, Recherches microscopiques sur le syst<^me 62, &c. This symmetry must appear highly astou- 

 nerveux, Copenhague, 1844, p. 72; fViU, Vorlau- ishiug. 



fige Mittheilung über die Struktur der Ganglien 3 These prolongations give the ganglionic gtob- 



und den Ursprung der Nerven bei wirbellosen ules a clavate aspect, as already seen and figtu-eti 



Thieren, in Mailer's Arch. 1844, p. 82 ; Ehren- by Ehrenberg (loc. cit. Tab. VI. fig. 7, and Sg. 



berg, Beobachtung einer auffallenden, bisher uner- 7."-, IJ'^). 



kannten Struktur des Seelenorgans bei Menschen Further researches must decide if these prolbn- 



und Thieren, in the Abhandl. d. Berl. Akad. 1834, gations are really continuous with the primitive 



p. 720, Tab. VI. fig. 7 ; and Falentin, Ueber den nervous fibres, as Heimholtz (loc. cit. p. la), aiid> 



Verlauf und die letzten Enden der Nerven, in the Hannover (loc. cit. p. 73, Tab. VI. fig. 78), affirm 



Nov. Act. Acad. XVIII. 1836, p. 202, Tab. to l)e the case ; for, Valentin in his apparently so 



Till. careful researches, has never seeu any trace of -a 



2 Valentin declares that he has seen in the brain clavated or pedunculated ganglionic globule.* 



* [ § 147, note S.] This alleged relation of the Leydig, an excellent observer, confirms the geo- 



elements of the nervous tissue is a point of no Uttle eral view here advanced of the direct connection 



histological importance and I shall give it a special of the ganglionic globule wjth the nerve-tube ; see 



consideration in noticing the minute structure of loc. cit. p. 130, Taf. X. fig. 67 (_Piscicola). See 



this tissue with the higher animals. I have made also Bruch, Siebold and Kölliker'>s Zeitsch. 18491, 



no observations on the animals in question, but p. 175, Taf. XII. fig. 7, 8, 9. — Ed. 



14 



