USEFUL INSECTS 203 



captives, at best troublesome, though most interesting, will 

 probably disappear from the human association. 



With the silkworms, variations can be more readily 

 brought about ; for, as is the case with other animals, the 

 individuals can be paired. The efforts at selection already 

 made show that valuable characters can be thus accumulated, 

 thoueh not with the succe:3s which attends the efforts of a 

 like nature made in the case of our domesticated mammals 

 and birds. In common with other animals — indeed, we may 

 say, with all organic life — ^the silkworms vary perceptibly 

 in different parts of the world to which they may be taken. 

 Thus, when reared in California it is said that this insect 

 develops more strength than it exhibits in Europe ; and the 

 eggs which it lays there produce stronger insects, which 

 in turn vield larger cocoons than the individuals born in 

 Italy or France. With such a basis for the selective art 

 as the variations of this insect afford, there seems no rea- 

 son why it should not afford a good field for the work 

 of the breeder's art. 



