INTRODUCTION. 29 



parent, it is nourished as if it were one of its organs, and when it 

 detaches itself, it possesses its own life, which is essentially similar 

 to that of the adult. 



The germ, the embryo, the fcetus, and the new-born animal, have 

 never, however, exactly the same form as the adult, and the differ- 

 ence is sometimes so great, that their assimilation has been termed a 

 metamorphosis. Thus, no one not previously aware of the fact 

 would suppose that the caterpillar is to become a butterfly. 



Every living being is more or less metamorphosed in the course 

 of its growth ; that is, it loses certain parts, and developes others. 

 The antennae, wings, and all the parts of the butterfly were enclosed 

 beneath the skin of the caterpillar ; this skin vanishes along with the 

 jaws, feet, and other organs, that do not remain with the butterfly. 

 The feet of the frog are enclosed by the skin of the tadpole ; and 

 the tadpole, to become a frog, parts with its tail, mouth, and bran- 

 chiae. The child, at birth, loses its placenta and membranes ; at a 

 certain period its thymus gland nearly disappears, and it gradually 

 acquires hair, teeth, and beard ; the relative size of its organs is 

 altered, and its body augments in a greater ratio than its head, the 

 head more than the internal ear, &,c. 



The place where these germs are found, and their germs them- 

 selves are collectively styled the ovary; the canal through which, 

 when detached, they are carried into the uterus, the oviduct; the 

 cavity in which, in many species, they are compelled to remain for 

 a longer or shorter period previous to birth, the uterus. 



Of the Intellectual Functions of Animals. 



The impression of external objects upon the individual, the pro- 

 duction of a sensation or of an image, is a mystery into which the 

 human understanding cannot penetrate; and materialism an hypo- 

 thesis, so much the more conjectural, as philosophy can furnish no 

 direct proof of the actual existence of matter. The naturalist, 

 however, should examine what appear to be the material conditions 

 of sensation, trace the ulterior operations of the mind, ascertain to 

 what point they reach in each being, and assure himself whether 

 they are not subject to conditions of perfection, dependent on the 

 organization of each species, or on the momentary state of each 

 individual body. 



To enable a being to perceive, there must be an uninterrupted 



