DIVISIONS OF THE ANIMAL KINGHOM. Ixiii 



the members of a common stock. When two animals of dis- 

 similar characters breed together, the progeny partake of the 

 properties of both parents. It is only by continued repro- 

 duction between their descendants, that a common class of 

 characters is acquired, and a true variety formed ; and the 

 longer this successive reproduction and intermixture of blood 

 are carried on, the more permanent may the transmitted 

 characters be supposed to become. 



It appears, too, that the nearer animals are allied in blood, 

 the more quickly is the similarity of characters distinctive of 

 a breed acquired. In the practice of English breeders, it has 

 not been uncommon to unite brothers with sisters, and pa- 

 rents with their direct progeny, and to carry on this system 

 for a long period. The physiological effect is remarkable, 

 not only producing more quickly that community of charac- 

 ters which constitutes a breed, but affecting the temperament 

 and constitution of the animals. Under this system long 

 continued, the animals manifest symptoms of degeneracy, as 

 if a violence had been done to their natural instincts. They 

 become, as it were, sooner old ; the males lose their virile" 

 aspect, and become at length incapable of propagating their 

 race, and the females lose the power of secreting milk in suf- 

 ficient quantity to nourish their young. These effects may 

 not for a time be very observable, but, by carrying on the 

 system sufficiently far, they never fail to manifest themselves. 

 Dogs continually reproduced from the same litter exhibit, 

 after a time, the aspect of feebleness and degeneracy. The 

 hair becomes scanty, or falls off, the size diminishes, the 

 limbs become slender, the eyes sunk, and all the characters 

 of early age present themselves. Hogs have been made 

 the subjects of similar experiments. After a few generations, 

 the victims manifest the change induced in the system. They 

 become of diminished size, the bristles are changed into hair, 

 the limbs become feeble and short, the litters diminish in 

 frequency and in the number of the young produced, the 

 mother becomes unable to nourish them, and, if the experi- 



