ENCEPIIALON OF FISHES. 287 



modifications for retaining water in contact with the gills, so 

 characteristic of the Apodal, the Lophioid, and Labyrinthi-branch 

 fishes, are remarkable, nevertheless, for their tenacity of life out 

 of water ; and the peculiarly developed vagal lobes may relate to 

 this maintenance of the power of the respiratory organs during a 

 suspension of their natural actions. 



The extensive gradation of the cerebellum between the ex- 



c? 



tremes of structure presented by the Myxine and the Shark, 

 as might be expected, throws more direct light upon its function. 

 With regard to this, two views have been taken. According to 



O * O 



one it is the organ of amativeness ; according to the other it is 

 the seat of the muscular sense, or the regulator of voluntary 

 motion. Many experiments in which the cerebellum has been 

 mutilated or removed in warm-blooded animals support the idea 

 of its intimate relation with the locomotive powers. But to the 

 conclusions from these experiments has been objected the pos- 

 sibility of the convulsive muscular phenomena having arisen from 

 the stimulus on the remaining centres, occasioned by the mutilation 

 or destruction of the one in question ; and it may well be doubted 

 whether Nature ever answers so truly when put to the torture, 

 as she does when speaking voluntarily through her own experi- 

 ments, if we may so call the ablation and addition of parts which 

 comparative anatomy offers to our contemplation. 



If, in reference to the sexual hypothesis of the cerebellum, we 

 contrast the Lamprey with the Shark, we shall be led, by the 

 much larger proportional size of the generative organs in the 

 lower cartilaginous Fish, and from the observed fact of the male 

 and female Lampreys entwining or wreathing themselves entirely 

 about each other, mutually aiding in the expulsion of their 

 respective generative products, and so absorbed in the passion as 

 to permit themselves to be taken out of the water and replaced 

 there, without interruption of the act, to expect a larger cere- 

 bellum in the Lamprey than in the Shark. But the very re- 

 verse of this is the fact : the Lamprey has the smallest, and 

 the Shark the largest, cerebellum in the class of Fishes. If, 

 on the other hand, we compare the Cyclostome and Plagio- 

 stome Cartilaginous Fishes, in reference to their modes and 

 powers of locomotion, we shall find a contrast which directly 

 accords with that in their cerebellar developement. The Myxine 

 commonly passes its life as the internal parasite of some higher 

 organised fish : the Lamprey adheres by its suctorial mouth 

 to a stone, and seldom moves far from its place : neither fish 

 possesses pectoral or ventral fins. The Shark, on the contrary, 



