DISEASES OF THE OX AND SHEEP. 639 



creatures, like generally gives origin to like, whether it be plant 

 or whether it be animal, we see in miniature and on a very small 

 scale an exemplification of a wide and far-reaching truth. In 

 accordance with this law of reproduction, the great and won- 

 drously complex world of living organisms, of which huge 

 pyramid, so to speak, we human beings form as it were the 

 highest point or apex, continues to maintain its rhythmically 

 interrupted existence from era to era of the world's history, 

 from 8eon to aeon. 



We have said that the lowest living things reproduce their 

 kind for many successive generations by simply splitting up into 

 two or more portions, each of which assumes an independent 

 existence forthwith, and that this is true in regard to both 

 animals and plants of very low type. As we gradually advance, 

 so to say, up the ladder made up by the innumerable forms of 

 life, we see that instead of actual division or fission, the process 

 of budding or gemmation above mentioned becomes more and 

 more distinctly marked, while coincidently a differentiation 

 betwixt the two sexes occurs. Then, as we ascend the scale of 

 existence, and especially that of animal life, we find the pro- 

 cesses of fission and gemmation become less and less frequent, 

 and the two sexes gradually becoming more and more diffe- 

 rentiated from each other, neither of them multiplying by 

 fission or by gemmation, and one sex definitely supplying the 

 ovum or egg, the other definitely furnishing the sperm cells 

 whereby the egg is fertilised. 



Ascending still higher the tree of animal life, we are succes- 

 sively confronted with new and more complex factors, until in 

 the highest animals, the mammals, the functions of reproduction 

 of their kind is one of most serious and grave moment, and 

 apparently often of such great importance as to override nearly 

 all other considerations. In the female a special cavity is 

 formed, and set apart for the developing foetus. Herein the 

 foetus is contained, and it is supplied with nourishment from the 

 mother, until sufficient strength has been gained to enable it to 

 fight its own way in the world by the aid of the help still 

 supplied by its parents. It is then expelled from the mother's 

 womb, but by no means is it yet left entirely to its own unaided 

 resources. On the contrary, the new-born creature, thus 

 unwittingly introduced into this marvellous world of ours, is 



