218 LECTURE VIU. 



and no irritant to the body has any effect on the electric organs any 

 more than it would have under the like circumstances on the muscles. 

 But, if the ends of the nerves in connection with the organ be irri- 

 tated, the discharge of electricity takes place, just as irritating the 

 end of the divided motor nerve in connection with muscle would 

 induce its contraction. If part of the electric nerves be left in con- 

 nection Avith the brain, the stimulus of volition cannot, through these, 

 excite the discharge of the whole organ, but only of that part of the 

 organ to which the undivided nerves are distributed. So, likewise, 

 the irritation of the end of a divided nerve in connection with the 

 electric apparatus, excites the discharge of only that part to which 

 such nerve is distributed. "We have seen that the power of exciting 

 the electric action, like that of exciting the muscular contraction, is 

 exhausted by exercise and recovered by repose : it is also augmented 

 by energetic circulation and respiration ; and what is more signi- 

 ficative of their close analogy, both powers are exalted by the dii-ect 

 action, on the nervous centres, of the drug ' strychnine : ' its appli- 

 cation causes simultaneously a tetanic state of the muscles of the 

 fish, and a rapid succession of involuntary electric discharges. * 



The survey of the nervous system of fishes cannot be concluded 

 without a notice of two systems of mucous organs in intimate con- 

 nection with the nerves of sensation ; one system is common to the 

 Torpedo with other Plagiostomes ; the other system is peculiar to the 

 Torpedo, in which it was discovered by Prof. Savi. 



The first or muciferous system consists of the long slender mucous 

 tubes {fig. 45. m), which, commencing by groups of globular vesicles 

 (ib. »i.) situated in the Torpedo, symmetrically at the forepart of the 

 head and outside the electric organs, run in parallel fasciculi from which 

 the tubes, successively detaching themselves, perforate the skin, and 

 terminate by orifices, some at the dorsal, some at the ventral surface, 

 between the outer border of the electric organs and that of the body 

 of the animal. A considerable filament of the ganglionic portion of 

 the trigeminal nerve expands upon the ampulliform commencement 

 of each of the muciferous tubes : the nerve may receive impressions 

 conveyed to it by the tube and its clear jelly-like contents, or it may 

 preside over the secretion of those contents, or combine both func- 

 tions. 



The second or follicular system consists of linear series of minute 

 subcutaneous svibsphei'ical cells, situated at the anterior part of the 

 head of the Torpedo, chiefly on the under surface : each cell has a 

 double membranous tunic, and contains a grey cerebriform matter ; 



* Lxxvi. 13. 162. 



