216 CLASS VII. 



The Nervous System in the Annulata proper consists, as in 

 Insects, of ganglia connected by two cords and placed behind each 

 other in a series in the middle of the body on the abdominal sur- 

 face. Originally each ganglion consists of two lateral portions, as 

 is proved by the process of development : on the regeneration also 

 of parts that have been cut away the nervous system appears to be 

 formed of two lateral portions. A larger ganglion lies in the head, 

 and is connected, by two nervous threads that form a ring around 

 the oesophagus, with the first ganglion of the abdominal chain. 

 But the Nervous System presents much variety in different genera, 

 as well in the number as in the greater or less development of the 

 ganglia and in the nerves that spring from them ; whilst in the 

 earth-worm, for instance, the numerous ganglia of the abdominal 

 chain almost touch each other, in the leech they are only twenty- 

 four or twenty -five in number, and are placed far asunder, especially 

 in the middle. In Pleione carunculata the Nervous System con- 

 sists, according to GRUBE, besides the middle chain, of two lateral 

 cords, also with ganglia, which are connected with the former by 

 transverse threads 1 . In Eunice sanguinea QUATREFAGES found 

 minute ganglia at the base of the rudimentary feet, which however 

 were not connected, as a chain, by longitudinal filaments. In ad- 

 dition to this nervous apparatus a special nervous system has been 

 detected in many instances, agreeing with that portion of the 

 nervous system in Insects which has been compared to the Nervus 

 sympathicus of the higher animals : of which we shall treat more 

 at large at the class of Insects. In Hirudo medicinalis BRANDT 

 discovered three minute ganglia in the head, which are united by 

 threads with the cerebral ganglion, and from which the maxillary 

 nerves arise ; with the middlemost of the three ganglia a nerve is 

 probably in connexion, which runs beneath the stomach in a longi- 

 tudinal direction and finally divides into two branches ; but this 

 nerve differs from the sympathetic of insects in respect of its 

 position on the inferior surface. In Eunice sanguinea and some 



1 Diss. zootom. de Pleione carunc. p. 9, figs, i, 5. STANNIUS (his, rSsi) observed 

 the same thing in another species of Pleione (Amphinome rostrata). It is as though there 

 were a repetition of the form of the vascular system on the dorsal surface, which here 

 consists of three stems; see above (p. 212). Perhaps this arrangement occurs in 

 several Annulata; at least WAGNER describes it also in Pontobdella muricata, Lehrb. 

 der vergl. Anat. 1835, s. 381. 



