332 ANIMAL NATURE AS A WHOLE. [in. 



fall into the error of those who thus argue (Baumgarten^s 

 ' Metaphysics/ § 576), and say — contrary to the ordinary 

 meaning of terms — that a tortoise, which crept about for six 

 months, deprived of its head; or that a headless butterfly, 

 which had sexual intercourse, and deposited its ova ; or that a 

 snail, similarly mutilated, which sought about for food, and had 

 its head regenerated ; or that a lizard that ran about in the 

 grass for several days after decapitation, &c., was a dead 

 animal, or a corpse. 



644. The life of every animal is divided into four periods. 

 The first is the period of development^ and extends from the 

 moment at which the germ is separated from the parent, to the 

 time when it is so far developed as to be capable of an inde- 

 pendent existence. In the majority of animals this occurs at 

 birth. 



645. The second period is i\LQ period of growth, and extends 

 from the moment of birth to the time when the animal is fully 

 developed, and fit for the performance of the entire range of 

 its functions, and of those duties which nature has assigned it. 

 During this period the animal is unfit for many functions which 

 it performs afterwards, when fully developed. 



Qi^Qt. Neither nutrition nor growth are purely animal func- 

 tions, nor do they involve animal machines only, but are effected 

 by the common action of the forces of all parts of the entire 

 nature of an animal, — the physical, mechanical, organic, and 

 animal — and in sentient animals — the animal-sentient forces — 

 all acting in wonderful union to that end. 



Note. — The laws of nutrition and growth are laid down in 

 physiological works, and we refer to them here only in so far 

 as they bear on proper animal nature, and influence the proper 

 animal machines, and the proper animal forces. 



647. Neither the nerves, nor, in sentient animals, the brain, 

 are fully developed at first, or are fully capable of the vis 

 nervosa, or of all the animal-sentient forces. Innumerable 

 facts show, not only that the nerves continue to grow after 

 birth, but are developed in new growths. This is most clearly 

 seen in insentient animals, as in insects ; in the metamorphoses 

 they undergo during the various stages of their development ; 

 and in animals in which entire limbs, or entire segments of the 

 body, have been reproduced after mutilation. 



