xxii INTRODUCTION. 



neither smell, nor see, nor hear ; and in proportion as these senses 

 in different animals are acute, so we find the nervous structures 

 of their individual organs to be more or less developed. The 

 nerves belonging to the sensitive organs are not included in 

 the foregoing classes: possessing the peculiar faculties of taking 

 cognizance of odour, light, and sound, they differ as much from 

 the nerves of common sensation as Sir Charles Bell has demon- 

 strated the latter to do from those of motion. 



Exclusively of the nervous influence, the anatomical mechanism 

 of the several organs included in the sensitive system, is no less 

 wonderfully than admirably adapted to those ends which, in 

 each of them, it is designed to answer ; and rises far more beyond 

 all human art and contrivance than it is possible for the mind of 

 man to conceive. That the hound should be able, with fatal 

 fidelity to his prey, to pursue the evanescent odour of footsteps, 

 is owing to a faculty possessed by the nose ; but one equally 

 inexplicable to us, with the extraordinary telescopic and micro- 

 scopic powers possessed by the eye, or the finer and more delicate 

 sense inhabiting the ear. 



The term of life of every animal being limited to a more or 

 less distant period, according to its kind, it became necessary, 

 in order to guard against annihilation, to make provision for the 

 procreation of the species. In the higher classes of animals, 

 generation is effected by concurrence of the sexes, the organs for 

 the purpose being different in them respectively, though recipro- 

 cally adapted to the same end ; but in some animals of a lower 

 grade, the sexes are found combined in the same individual, and 

 generation takes place without any copulative act whatever. In 

 the animals by which we are surrounded in common life, we find 

 a male and female sex ; and these are distinguished, in an ana- 

 tomical point of view, by the possession of organs of a totally dif- 

 ferent character. In the male we have the testicles, which secrete 

 the peculiar fluid from the blood, known by the name of semen ; 

 and the penis, an organ formed for the conveyance and transmis- 

 sion of the semen into the womb of the female ; besides seminal 

 ducts and reservoirs to contain the fluid until it is wanted. In the 

 female we find a vagina or canal leading into the uterus or womb ; 

 attached to the horns of which by two serpentine tubes, called 



