THE CESTROUS CYCLE IN THE MAMMALIA 47 



similar animals in the wild state that the sexual periods 

 are likewise restricted. Raciborsky l says that in the more 

 domestic types of cattle the cows receive the bull more 

 frequently than in the wilder breeds. Ellenberger 2 states that 

 among domestic cattle the dicestrous cycle varies from about 

 two to four weeks, but Schmidt 3 has shown that the differences 

 may be much greater. Wallace 4 says that oestrus recurs in 

 summer every nineteenth day, but in winter it may not recur 

 oftener than every twentieth or every twenty-first day. Usually 

 the cow seeks the bull again four or five weeks after calving. 

 Shortt, 5 however, states that in India this does not occur until 

 after six or nine months. Blood is not infrequent in the ex- 

 ternal procestrous discharge of cows and heifers. Emrys-Roberts 6 

 has described the internal generative organs of a prooestrous 

 cow as containing a watery secretion tinged with blood. The 

 secretion was found to contain far less mucin than during the 

 ancestrous period. 7 



The period of gestation in cattle is about nine months, but 

 it is slightly variable. 



According to Heape, who has collected evidence from various 

 authorities, the ibex, markhor, barasingha, and Hemitragus 

 jemlaicus in Cashmir, as well as the American bison, black- 

 tailed deer in Montana, red-deer, fallow-deer, and roe-deer, 8 and 



1 Raciborsky, Traite de Menstruation, Paris. 



2 Ellenberger, loc. cit. 



3 Schmidt, " Beitriige zur Physiologie der Brunst beim Rinde," Disserta- 

 tion, Zurich, Miinchen, 1902. 



4 Wallace (R.), loc. cit. 



5 Shortt, A Manual of Indian Cattle and Sheep, 3rd Edition, Madras, 

 1889. 



6 Emrys-Roberts, " A Further Note on the Nutrition of the Early Embryo, 

 &c.," Proc. Roy. Soc. B., vol. Ixxx., 1908. 



7 According to Emrys-Roberts, the profuse mucinous secretion during the 

 prooestrum in the Mammalia is derived, not from the body of the uterus, 

 but from the cervix and vagina. 



8 There has been some controversy regarding the breeding season and 

 period of gestation in roe-deer. According to Bischoff (Entivicklungsgeschichte 

 de.s Rehcs, Giessen, 1854) rut occurs in early autumn, but the embryo is not 

 developed beyond the stage of segmentation in the following spring. Groh- 

 mann (Sport in the Alps, Edinburgh, 1904) says that rut is experienced in 

 July and the beginning of August, but that there is a "false rut" in 

 November. Observations on roe-deer in Vienna showed that the period 

 of gestation is ten months ; for seven females which were served by one 



