524 ON PARTURITION. 



the time which is described by these ; also the motions of the 

 moon for these are the common origin of generation to all. 

 For it is in accordance with reason that the cycles of inferior 

 things should follow those of the higher." Nature, then, has 

 decreed that the birth and death of animals should have their 

 period and limit after this manner. 



. Just as the birth of animals depends on the course of the 

 sun, and moon, so have they various seasons for copulation and 

 different terms of utero-gestation, these last being longer or 

 shorter according to circumstances. " In the human species 

 alone," says the philosopher in the same part of his works, 

 " is the period of utero-gestation subject to great irregularity. 

 In other animals there is one fixed time, but in man several ; 

 for the human foetus is expelled both in the seventh and tenth 

 months, and at any period of pregnancy between these; more- 

 over, when the birth takes place in the eighth month, it is pos- 

 sible for the infant to live." In the majority of animals there 

 is a distinct season for bringing forth their young ; this is 

 generally found to be in the spring, when the sun returns, but 

 in many species it is in the summer, and in some in the 

 autumn, as is the case with the cartilaginous fishes. Hence it 

 is that animals, as the time of labour approaches, seek their 

 accustomed haunts, and provide a safe and comfortable shelter 

 where they may bring forth and rear their young. Hence, too, 

 the title "bird-winds," applied to those gales which prevail toward 

 the beginning of spring, the word owing its origin to the fact 

 of certain birds at that period of the year availing themselves 

 of these winds to accomplish their migrations. In like man- 

 ner stated seasons are observed by those fishes which congre- 

 gate in myriads in certain places for the purpose of rearing 

 their young. Moreover, in the spring, as soon as caterpillars 

 fall under our notice (their ova, as may be observed by the 

 way, like to invisible atoms, being for the most part carried by 

 the winds, and not owing their origin, as commonly supposed, 

 to spontaneous generation, or to be looked upon as the result 

 of putrefaction), straightway the trees put forth their buds, 

 soon to be devoured by these creatures ; and these in their 

 turn fall victims to birds innumerable, and are carried to the 

 nest as food for the young brood. So constantly does this 

 hold, that whenever strange species of caterpillars fall under 



