^v§, 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 animals, 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 oif 

 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 



§ 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 splanchnicus). 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 Ilirudinei only ; see globules, that those of the two lateral halves cor- 

 Helmholtz, De fabrica systematis nervosi everte- responded exactly as to number, volume and posi- 

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

 ver, Recherches microscoi)iques sur le systiime 62, &c. This symmetry must appear highly astou- 

 nerveux, Copenhague, 1344, p. 72; JVill, Vorlau- ishlng. 



flge Mittheilung uber die Struktur der Ganglien 3 These prolongations give the ganglionic glob- 



und den Ursprung der Nerven bei wirbeliosen ules a clavate aspect, as already seen and figured 



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



berg, Beobachtung einer auffallenden, bisher uner- 7.'l', 7. '2). 



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



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



p. 720, Tab. VI. fig. 7 ; and Valentin, Ueber den nervous fibres, as Helmholtz (loc. cit. p. 15), and 



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 be the case ; for, Valentin in his apparently so 



VIII. careful researches, has never seen any trace of a 



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



* [§ 147, note 3.] This alleged relation of the Leydig, an excellent observer, confirms the gen- 

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

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

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

 this tissue with the higher animals. I have made also Bruch, Siebold and Kijlliker\i Zcitsch. 1849, 

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



14 



