98 THE PERFECT HORSE. 



quota to the formation of the embryo^ it is reasonahle to 

 expect that each shall he represented in it j which is 

 found to he the case in nature, But^ as the food of the 

 emhryo entirely depends upon the mother,^ it may he 

 expected that the health of the offspring^ and its constitu- 

 tional poioers^ will he more in accordance with her state 

 than with that of the father : yet,, since the sire furnishes 

 one-half of the original germ,, it is not surprising^ that,, 

 in external and general character,, there is retained a 

 FACSIMILE, to a certain extent^ of him. 



" 8. The ovum of mammalia differs from that of birds 

 cliiefly in the greater size of the yolk of the latter, be- 

 cause in them this body is intended to support the 

 growth of the embryo from the time of the full forma- 

 tion of the egg until the period of hatching. On the 

 other hand, in mammalia the placenta conveys nourish- 

 ment from the internal surface of the uterus to the em- 

 bryo during the whole time which elapses between the 

 entrance of the ovum into the uterus and its birth. 

 This period embraces nearly the whole of the interval 

 between conception and birth, and is called utero-gesta- 

 tion. 



*' 9. In all THE mammalia THERE IS A PERIODICAL 



'iiEAT,' marked by certain discharges in the female, 

 and sometimes by other remarkable symptoms in the 

 male (as in the rutting of the deer). In the former it 

 is accompanied, in all healthy subjects, by the descent 

 of an ovum, or ova, into the uterus ; and in both there 

 is a strong desire for sexual intercourse, which never 



