624 Dynamic Theory. 



ters, through the force of a necessary habit of work extending over a 



long time. 



It has been supposed by some that the cerebellum is the seat of the 

 sexual instinct. If so, it ought to be well developed in proportion to 

 the intensity of the instinct. But this is not the case in fishes, for 

 some, having the strongest instinct in this direction, have the smallest 

 cerebellum, as, for example, the lamprey, whose cerebellum is a mere 

 transverse band of medullary matter, is nevertheless endowed with a 

 very intense sexuality. The same is true of other fishes. The rapid 

 development of the cerebellum at a very early period of life, when such 

 development can surely have nothing to do with the maturing of sexual 

 powers, and which anticipates b}^ a long period the maturing of the sex- 

 ual organs, is a strong fact against the theory. 



The brain is subject to the same law of development by use, and loss 

 or atrophy by disuse, that governs all other organic tissues. Accord- 

 ing to this law, if the theory in question be true, we ought to find a re- 

 duction of the cerebellum in those animals in which the sexual function 

 is destroyed artificially. A series of observations on the brains of 

 horses, show that early emasculation does not tend to diminish the de- 

 velopment of the cerebellum. 



The following table embodies the results of observations on the brains 

 of 10 stallions from 9 to 17 years old, 12 mares from 7 to 16 years old, 

 21 geldings from 7 to 17 years of age. ( Carpenter's Physiology.} 



From this table it appears that the cerebellum of the gelding averages 

 nearly i higher in absolute weight than that of the stallion or mare, and 

 that its proportion to its own cerebrum is likewise greater by about i. 

 The absolute average weight of the cerebrum is considerably less in the 

 gelding than in the stallion ; so that we might be led to suspect that 

 the cerebrum has more to do with the sexual functions than the cerebel- 

 lum. The additional size of the cerebellum attained by the gelding, is 

 attributed to the fact that animals of this class are taught a greater 

 command of their muscular powers, and are subject to a greater disci- 

 pline and activity, bringing out a greater versatility in the exercise of them. 



