GENERATION OF ANIMALS, II. vii.-viii. 



as is proved by the fact that this is the only region 

 which unmistakably changes its appearance during 

 sexual intercourse, and those who overfrequently 

 indulge in it have noticeably sunken eyes. The 

 reason is that the nature of the semen is similar to 

 that of the brain " ; its matter is watery whereas 

 its heat is a mere supplementary acquisition.* Also 

 the seminal discharges come from the diaphragm, 

 because the first principle of the natural organism is 

 there, '^ so that the movements initiated in the genital 

 organs penetrate to the chest, and the scents from 

 the chest become perceptible through the breathing. 



As I said earlier, this particular deformity occurs Mules, 

 in man and in the other kinds of animals to some 

 extent, but \\ith mules it is the whole race that is VIII 

 infertile. What Empedocles has to say about the 

 reason for this is obscure ; Democritus is more intel- 

 ligible ; but they are both wrong. They give one 

 omnibus explanation, covering all cases of copulation 

 between animals of different kinds. Democritus '^ 

 says that in mules the genital passages are destroyed 

 in the uterus, because the formation of these animals 

 has its origin in parents of different species. But we 

 find this same situation with other animals, and 

 yet they generate notwithstanding ; whereas, if 

 Democritus's explanation was right, all other animals 

 which unite in this way ought to be infertile too. 

 The cause alleged by Empedocles is this : He says « 

 the mixture of the seeds becomes dense as a result of the 

 tno component portions of semen being both soft ; because, 

 the hollows of one ft into the densities of the other, and in 



» See Introd. § 69. ' See 719 a U. 



'' See Diels, Vorsokr.'^ 68 A 151. 



■= Diels, Vorsokr.^ 31 B 9:2 ; c/. 91 ; and 31 A 82. 



249 



