IH. I.] ACTION OF THE VIS NERVOSA. 213 



msation and after decapitation. {Vide §§ 172 — 176 and 209 — 

 115.) The cortical substance of the brain is to be classed with 

 le secreting organs. 



395. The functions of the sexual organs both in the male 

 id female are carried on not solely by means of the cerebral 



"forces^ but often through the vis nervosa only, as experiments 

 on decapitated animals demonstrate (357). 



396. The movements of the limbs display the influence of 

 the vis nervosa strikingly, because its action is greatest on the 

 muscular portion of the organism. These, as a thousand ex- 

 periments prove, may arise as nerve-actions, although they 

 usually occur as sentient actions from external sensations and 

 sensational conceptions, instincts, and passions, as well as 

 volitionally. Thus, a decapitated animal will stand, move for- 

 wards, raise itself up, leap, fly, or flutter its wings, seek food, 

 clean, defend or conceal itself, copulate, &c. A decapitated 

 man immediately after decapitation struggles to free his hands, 

 attempts to stand upright, and to stamp with his feet ; if the 

 head of a pigeon be cut ofi* whilst it is running, it continues 

 to run on for some distance, until it knocks against something ; 

 a frog leaps forward without its head, so also a headless fly flies, 

 a snake, a fish, a worm, writhes and twists about, if touched, 

 although wholly deprived of sensation ; a fly makes the move- 

 ment of brushing its eyes by a natural instinct, although its 

 head be cut off^; a headless snail seeks its food by its usual 

 plan of feeling about; a decapitated tortoise does the same 

 thing, and will live for half a year after decapitation, and raise 

 itself up, or endeavour to do so if placed on its back ; an ear- 

 wig nips with the nippers of its abdomen at its own separated 

 head, when the head bites the abdomen; the abdomen of a 

 wasp will sting; animals that fight with their hind feet use 

 them vigorously when decapitated, at every irritation applied to 

 the nerves; butterflies, caterpillars, and silk-worms copulate 

 after decapitation, and they and flies deposit their ova; in 

 short, all the instinctive actions of animals are sometimes seen 

 to occur as nerve-actions; and it naturally follows that they 

 occur at first in newly-born animals as such, and that it is only 

 after the perception of external sensations that they become 

 sentient actions (269). 



397. Thus the dominion of the vis nervosa is in reality as 



