$$ 147, 148., THE ANNELIDES. 157 
laterally, thus forming a ring (the cesophageal ring) through which the 
cesophagus passes. 
§ 147. 
The histological elements of the nervous system of these anials, 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 ceptral 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 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 
nervous system of the Annelides is as yet based 
upon researches of that of the Hirudinei only ; see 
Helmholtz, De fabrica systematis nervosi everte- 
bratorum dissertatio. Berol. 1842, p. 12 ; Hanno- 
ver, Recherches microscopiques sur le systéme 
nerveux, Copenhague, 1844, p. 72; Will, Vorliu- 
fige Mittheilung iiber die Struktur der Ganglien 
und den Ursprung der Nerven bei wirbellosen 
Thieren, in Muller’s Arch. 1844, p. 82; Ehren- 
berg, Beobachtung einer auffallenden, bisher uner- 
kannten Struktur des Seelenorgans bei Menschen 
und Thieren, in the Abhandl. d. Berl. Akad. 1834, 
p. 720, Tab. VI. fig. 7 ; and Valentin, Ueber den 
Verlauf und die letzten Enden der Nerven, in the 
Nov. Act. Acad. XVII. 1836, p. 202, Tab. 
Vill. . 
2 Valentin declares that he has seen in the brain 
*([§ 147, note 8.] This alleged relation of the 
elements of the nervous tissue is a point of no little 
histological importance and I shall give it a special 
consideration in noticing the minute structure of 
this tissue with the higher animals. I have made 
no observations on the animals in question, but 
14 
and ventral ganglia of the leech so regular and 
symmetrical an arrangement of the ganglionic 
globules, that those of ‘the two lateral halves cor- 
responded exactly as to number, volume and _posi- 
tion ; see Valentin, loc. cit. p. 208, Tah. VIII. fig. 
62, &c. This symmetry must appear highly aston- 
ishing. 
3 These prolongations give the ganglionic glob- 
ules a clavate aspect, as already seen and figured 
by Ehrenberg (loc. cit. Tab. VI. fig. 7, and fig. 
TAL, 7.12), 
Further researches must decide if these prolon- 
gations are really continuous with the primitive 
nervous fibres, as Helmholtz (loc. cit. p. 15), and 
Hannover (loc. cit. p. 73, Tab. VI. fig. 78), affirm 
to be the case ; for, Valentin in his apparently so 
careful researches, has never seen any trace of a 
clavated or pedunculated ganglionic globule.* 
Leydig, an excellent observer, confirms the gen- 
eral view here advanced of the direct connection 
of the ganglionic globule with the nerve-tube ; see 
loc. cit. p. 180, Taf. X. fig. 67 (Piscicola). See 
also Bruch, Siebold and Kélliker’s Zeitsch. 1849, 
p. 175, Taf. XI. fig. 7, 8, 9. — Ep. 
