BREEDING. 125 



not spoiled, as in the case of other dogs, by frequent wet- 

 tings. 



Of course a dog can not be kept clean unless provided 

 with proper surroundings. Every place where he is ac- 

 customed to lie should be ready for his reception. To his 

 bed especial attention must be paid. For a large part of 

 the year nothing equals good straw ; it is both warm and 

 clean. It should be changed before it gets very short and 

 broken up, when it packs and irritates the dog in many 

 ways, and before it becomes saturated with emanations 

 from the animal's skin, when it is unhealthy and harbors 

 vermin. Pine shavings make a good summer bed, but 

 are apt to cling to the dog when he leaves his resting- 

 place. 



Some disinfectant beneath the bed tends to preserve it 

 sweet and to keep away vermin. 



BREEDING. 



In the lowest animals there is no distinction of sexes, 

 and reproduction of the species is maintained by division 

 of existing forms, one becoming two or more separate 

 individuals. Among the invertebrates the two sexes are 

 in many groups united in one individual, a common ex- 

 ample of which is the tape-worm. In all vertebrates the 

 sexes are distinct, and copulation or its equivalent is the 

 rule. Both male and female furnish their quota to the 

 new being. To explain more fully, in the higher verte- 

 brates e. g., in the dog tribe the female organs of gen- 

 eration at definite periods undergo changes consequent on 

 a special accumulation of energy, resulting in the matura- 

 tion in the ovary of eggs (ova), which are discharged into the 



