SEX DETERMINATION IN CATTLE. 2O7 



oestrous cycle designated by Marshall 1 (p. 36) as the Procestrum 

 and (Estrus respectively. The combined period is called "heat" 

 in some cases, whereas in others only a portion of the period of 

 marked sexual activity is so designated. This fact, together 

 with the natural variability of the phenomenon itself amongst 

 different individuals, accounts for the rather widely varying 

 statements found in the literature regarding the duration of 

 "heat" in the cow. Leuckart 2 puts the duration for cow and 

 mare at "about" 4 days. Thury 3 implies a rather shorter 

 duration than this. Flemming 4 says regarding the matter: 

 'The frequency and duration of the period of 'rutting' or 'heat' 

 depends upon the age, species, and other circumstances; but 

 it may be said to persist in the domestic animals from I to 

 15 days at the most. The shortest period is witnessed in the 

 cow and sheep and the longest in the bitch. It is sometimes 

 only present from 12 to 24 hours in some non-fecundated ani- 

 mals." Diising 5 puts the time of active "heat" in cattle at 

 24-30 hours at the outside. This is the experience of practical 

 breeders generally. 



Under these circumstances it is not to be expected that the 

 returns discussed in this paper are absolutely accurate as to the 

 division of the cestrous period into early, middle, and later 

 portions. No sharp delimiting boundaries between these divi- 

 sions were, or could be, set in the schedules. The matter had 

 to be left to the judgment of the breeder. We have not been 

 able to discover any reason, however, for supposing the error 

 introduced from the indefiniteness of the phenomenon itself to 

 be biased in one direction or the other. There is unquestionably 

 overlapping of the divisions of the oestrous period in the returns, 

 but there is no reason to suppose that this is not as great pro- 

 portionately in one direction as in the other. The relation 



1 Marshall, F. H. A., "The Physiology of Reproduction," London, 1910. 



2 Leuckart, R., "Zeugung." In Wagner's " Handworterbuch der Physiologic," 

 Bd. 4, pp. 707-1101, 1853. 



3 Thury, M., "Ueber das Gesetz der Erzeugung der Geschlechter bei den 

 Pflanzen, den Thieren und dem Menschen," Leipzig, 1864. 



4 Flemming, Geo., "A Text-book of Veterinary Obstetrics," New York, 1879. 



6 Diising, C., "Die Regulierung des Geschlechtsverhiiltnisses bei der Vermehrung 

 der Menschen, Tiere und Pflanzen," Jenaische Zeilschr., Bd. 17, pp. 593-940, 1884. 



