158 



THE ANNELIDES. 



§US. 



ring, and others with the cerebral ganglion by means of other small gan- 

 glia near the cephalic extremity /^^ 



With the different orders and sub-orders of the Annelides, the nervous 

 system has the following modifications : 



1. The Nemertini differ remarkably from the other Annelides in this 

 respect ; for their ventral cord is without ganglionic enlargements, and 

 composed of two separated cords, one on each side of the body, which 

 send off", right and left, lateral branches along their course. These two 

 cords arise at the anterior extremity in two ganglia blended together above 

 the oesophagus, which represent the cerebral ganglion, and send off" many 

 nervous branches in front. <^' 



2. With the Hirudiuei, the ventral ganglia are much fewer than the 

 segments of the body, and are bound together by two contiguous cords. 

 The first and last of these ganglia are remarkable for their size. The first 

 sends filaments to the lips, the second to the caudal sucker. '^^ 



The Splandinic syston is composed of a small ganglion situated in front of 

 the cerebral one, and with which it is connected by two filaments. By its 

 gide are two others, which are also small and connect with the cerebral by 

 delicate threads. All three send branches to the oral parts, while a deli- 

 cate filament goes to the inferior surfiice of the intestinal canal, and repre- 

 sents an inner splanchnic nerve. ^''^ 



3. The ventral medulla of the Lumbricini consists of two nervous cords 



1 Brandt, Bemerkungen über die Mundmagen- 

 oder Eingeweide-uerven der Evertebraten. Leijizig 

 1835, p. 37. 



2 Rathke (Danzig. Schrift, loc. cit. p. IttO, Taf. 

 VI. tig. 10, 11) has thus described the nervous 

 system of Bor/asia striata. 



He has seen particularly two jiairs of cephalic 

 nerves arise from the cerebral ganglion. One and 

 the larger of these is principally distributed tu the 

 respiratory fossae of the head, while the other, the 

 smaller, passes directly in front, probably for the 

 vermiform organ upon the cephalic extremity. 

 Orsted (Beschreib, d. Plattwiirmer loc. cit. p. 5, 

 18), appears to be wrong in suspecting that Rathki 

 has taken the vascular for the nervous system, for 

 (^itatrefages (Icon, du E^gne anim. de Cuvier. 

 Zoophytes, PI. X.\XIV. fig. 1) has figured by the 

 side of the vascular system, the nervous system of 

 JVemerte.i Camil/ae, exactly as it is described by 

 Rathkf. 



3 See Brandt and Ratzehurg, Med. Zool. II. p. 

 250, Tab. XXIX. B. (iSamriiisuga medicinalis), 

 and Leo, in Mul/er's Arch. 1835, p. 42-2, Taf. XI. 

 fig. 10 {Piscicolagfometra). Wagner hn% found. 

 an arrangement quite different from the above, in 

 Pontobdella muricata (Isis, 1834, p. 131, 

 Taf. I. fig. 3). He saw here the ventral gan- 

 glia united by a single cord which sends off 

 from each side only a single nerve. This nerve, 

 after a short course, has a ganglion, and then 

 divides into lateral branches. According to Stan- 

 nius, these lateral branches are not united together 

 by longitudinal cords as is the case with the Am- 

 l)hinome.* 



■1 See Brandt, Med. Zool. II. p. 251, Tab. XXIX. 

 B. fig. 7, and, Bemerk, über die Mundmagennerven 

 loc. cit. p. 39 {Sa7igiiisuga medic inalis).\ 



* [ § 148, note 3.] Leydig (loc. cit. p. 129) has 

 found the structure of the cerebral nervous centre 

 of Piscicola, quite different from that as described 

 by L,eo. The cerebral mass is composed of cap- 

 sules containing ganglionic globules ; these cap- 

 sules are synunetrically situated on each side of 

 the median line, but are connected by a well- 

 marked trauaverse commissure composed of nerve- 

 fibres ; see Taf. X. 67, 68, 69. See also upon the 

 nervous system of the Leeches, Bruch (Ueber 

 das Nervensystem des Blutegels : Ein Beitrag zur 

 topographischen Histiologie des Nervensystems, 

 in Stebold and Kolliker\i Zeitsch. 1849, p. 164). 

 This memoir is ))riMcipally histological, and bears 

 »ipon that disputed point, — the alleged direct con 

 ncction between the ganglion-corpuscles and the 

 nurvc-fibres. It has, however, some topogra|)hical 

 anatomical details, and the accompanying figures 

 would ir.ake the whole subject very clear. — Kn. 



t [ § 148, note 4.] Bee, for some further remarks 

 on the Splanchnic system of the Hirudinei and 

 Lumbricini, Quatrefages, Ann. d. Sc. Nat. VILI. 

 1847, p. 36. According to him that of the Hiru- 

 dinei resembles that of the Insects, and is com- 

 posed of a chain of ganglia from which pass off 

 filaments, some to the abdominal chain, others to 

 the jaws, and others still to the walls of the oesoph- 

 agus. There is also a frontal ganglionic chaia 

 which forms in front a real arcade, and from 'srhicU 

 filaments are given off anteriorly. 



With the Lumbricini it is considerably different, 

 and he thinks unlike that which has yet been 

 described of all the other Annelides. 



See further, Ann. d. Sc. Nat. XIV. 1850, p. 282. 

 and XVIII. 1852, p. 167. 



See also Leydig, Siebold and Kölliker\i Zeitsch. 

 III. lift. 3, 1). 315, and (Quatrefages, Ann. d. ÖC 

 Nat. XVIII. 1852, p. 316 {Branchellion). — :Ei>. 



