DEVELOPMENT 277 



records that one important practical result of early mating 

 is that by following this practice a much larger number 

 of young are produced during the lifetime of the parent. 

 In producing hogs commercially, this advantage might 

 easily overcome any disadvantage arising from a reduc- 

 tion in the size of the mother. 



261. Gestation and lactation in relation to growth. 

 The two most important phenomena associated with 

 reproduction which might have a measurable influence on 

 growth are gestation and lactation. The period of gesta- 

 tion in the mammalian domestic animals is the period dur- 

 ing which the embryo is developing in the uterus, from 

 the fertilization of the egg until the young animal is 

 sufficiently matured to carry on an independent existence 

 outside the body of the mother. During this period the 

 unborn animal increases rapidly in size, and within its 

 tissues the processes of cell division, absorption and 

 assimilation proceed with exceptional energy. The nutri- 

 tion for the growth of the foetus during this period is 

 supplied entirely by the pregnant mother. The foetus 

 itself has no means of nourishing its own tissues. It is 

 wholly dependent upon the mother. To all intents 

 and purposes the young animal in the uterus is an organic 

 part of the body of the mother. The foetus is an enormous 

 parasite nourished by the mother through the circulation. 



It is a popular opinion among many breeders tliat 

 gestation is an exhaustive period for the mother, that 

 during this period the mother must not only provide for 

 her own physiological needs, but in addition must supply 

 the materials needed for the rapid development of the 

 foetus. It has been generally believed that because of 

 these facts the period of gestation is a severe strain on the 

 pregnant mother. If the mother herself has completed 



