O WALTER HEAPE. 



oestrus occurs during pregnancy it is probably diie to a 

 temporary diversion of a superabundant supply of placental 

 blood ; when it occurs at other times, the highly nutritious 

 food, with which the animals which experience it appear to 

 be generally supplied, or the condition resulting thereffom, 

 is possibly largely responsible for it. 



Metoestrum, or the Metcestrous Period. — If concep- 

 tion does not take place during oestrus the activity of the 

 generative organs gradually subsides during a definite period, 

 which I have called the metoestrum ; and this is followed, in 

 the simple form which we are now considering, by a long 

 period of rest. 



Anoestrum, or the Anoestrous Period, is the name I 

 have given to this period of rest. It may Inst two or three 

 or eleven or possibly more months, and during that time the 

 generative organs lie fallow in the non-pregnant female. It 

 is eventually succeeded by a new pro-oestrum, and the four 

 periods, pro-oestrum, oestrus, metoestrum, and anoestrum, con- 

 stitute what I have designated as the anoestrous cycle. 



By some this period of anoestrum is called the non-breed- 

 mg season, but this is not correct, for although conception 

 cannot take place during this period it may be occupied 

 partially or wholly by the period of gestation, and inasmuch 

 as gestation is included in the breeding season, the anoestrum 

 cannot be considered as a non-breeding season. 



We now have to consider a more complicated form of 

 sexual season. In this case the sexual season is ushered in 

 as before, with the pro-oestrum, oestrus follows, and is 

 succeeded by metoestrum, but instead of the anoestrum, a 

 short quiescent period now occurs which I have called the — ■ 



Dioestrum, or the Dioestrous Period.— This is a brief 

 period lasting only a few days, at the most probably not 

 more than twelve or fourteen days, while in some animals 

 four to six days may be its duration. It is followed at once 

 by a new pro-oestrum, and the four periods, pro-oestrum, 

 oestrus, metoestrum, and dioestrum, I have designated the 

 dioestrous cycle. 



