BREEDING. 127 



In all that relates to the sexual functions in the female 

 we have an illustration of the great law of periodicity of 

 rhythm. A bitch experiences these recurrences of sexual 

 activity at regular more or less fixed periods, usually twice 

 a year, and, though these may be delayed or shortened, 

 they are upon the whole very regular. 



Naturally the entire nature of the animal participates 

 in corresponding changes. Usually they are preceded by 

 a short interval of excitement, indicating the approach 

 of a more profound change. The mammary glands may 

 slightly enlarge ; the bitch, if young, may show rapid 

 growth ; some fall off in flesh ; the disposition is modified; 

 etc. The generative apparatus forming a connected 

 whole, it is not strange that the activity of the es- 

 sential organs (ovaries) is accompanied by a correspond- 

 ing increase in vascularity or blood supply of other 

 parts, so that the external genitals (vulva) enlarge. 

 There is a visible flow of mucus, to be soon followed 

 by blood. 



As soon as the ova are mature the female will accept 

 the male. This is not usually prior to the appearance of 

 blood, but may be before it has disappeared or soon after, 

 generally the latter. 



As there is nothing to show clearly that the period of 

 the coitus or service has anything to do with the sex of 

 the offspring, the bitch may be allowed to choose her own 

 time for congress with the male. 



As it is not possible to be certain that all the ova 



mature at one time, it is not irrational to allow of a 



second service after an interval of one or two days, 



though it is likely that if the first was in every way a 



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