DEVELOPMENT OF THE HOUSE. '21 



It may therefore be taken for granted that there is a certain 

 amount of danger at the end of the third and sixth weeks, but 

 that the most critical period is about the end of the seventh or 

 beginning of the eighth week ; for unless the villi appear in time 

 and succeed in coining into sufficiently intimate relation with 

 the uterine vessels, the developmental process is of necessity for 

 ever arrested. 



Concluding Observations. 



Evidently, from what I have already stated, breaking service 

 may be due either to abnormal development of the embryo or to 

 its surroundings being unsuitable. 1 



Nature may be said to have provided against what we call 

 breaking service. When one thinks of the millions of eggs pro- 

 duced in a single season by the cod and certain other fishes, one 

 is apt to suppose that there is no relation between the number of 

 ova and the wants of the species. On the other hand, the solan 

 goose lays but one egg a year, and the elephant may not mature 

 a score of eggs in a hundred years. I believe a mare may ripen 

 and shed from ten to twenty eggs during the year. If this is the 

 case, bearing in mind that the period of gestation is eleven 

 months, evidently in the mare provision has been made against 

 accidents during the earlier weeks of the breeding season. Con- 

 sidering first how the embryo may be concerned with breaking 

 service, I may point out that if the egg or the sperm has been in- 

 sufficiently nourished,, or, it may be, over nourished, the segmen- 

 tation of the egg may be abnormal; or, if this is successfully 

 accomplished, a feeble embryo may be the result — an embryo 

 with, it may be, a small allantois, or with an imperfect yolk 

 sac circulation, or an embryo incapable of anchoring itself to 

 the lining of the uterus. Or the embryo may reach the seventh 

 week, but either because the allantois is insufficiently developed, 

 or because it lacks the energy required to throw out the all- 

 important villi, the more permanent relations may never be 



1 In discussing this subject it will be best to take for granted that the mare 

 has settled, and held at least beyond the third week. It would be useless 

 to include mares which have never settled when dealing with this subject. 



