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 cesophagus, 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 Pletone 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'. In Hunice 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 Mirudo medicinalis Branpr 
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 m 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 Hunice sanguinea and some 
1 Diss. zootom. de Pleione carunc. p. 9, figs. 1, 5. Srannrus (Isis, 1831) observed 
the same thing in another species of Pleione (Amphinome rostrata). Itis 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. 
