Twin Pregnancy 401 



is absent. They tend to carry the twin fetuses to the regular 

 period as though but one were present, though, as already noted, 

 it is claimed that the duration of twin pregnancy is normally a 

 trifle less than that''of single pregnancy. 



In some cases there is an hereditary tendency to the production 

 of twins in a given strain or family and certain individual cows 

 produce twins year after year. Fleming quotes one case in 

 which a cow, during an interval of seven years, produced 25 

 calves, or an average of more than three per annum, having 

 given birth to a single calf the first time and thereafter pro- 

 ducing anywhere from two to six calves at a birth. In the one 

 instance of six young, all died prematurely. One of the most 

 notable cases of excessive numbers is that given in the Magazine 

 of Gurlt and Hertwig, Vol. 23, page 125. A cow which had 

 given birth to one vigorous calf was butchered, and fifteen 

 fetuses were found in the uterus. Other instances of from three 

 to six or more calves at a birth are recorded, scattered through- 

 out veterinary literature, and are of little interest, except from 

 the standpoint of curiosity, unless we should remark that, when 

 a cow is attended during parturition, a search of the uterus 

 should always be made, after the removal of one fetus, to de 

 termine the presence or absence of additional young. 



In the ewe, twins are very common and, in some of the large 

 mutton breeds, twin pregnancy becomes the rule and single 

 births the exception, aside from yearling ewes. In some well- 

 fed bands of ewes, we have seen an average of two lambs per ewe 

 for the entire number. In one case of 26 Cotswold ewes we ob- 

 served 52 lambs, there having been a sufficient number of trip- 

 lets to bring the average up to two lambs per ewe. 



In the smaller breeds of sheep, like the Merino, twins are less 

 frequent. 



In the goat, the general rule is twins or triplets. 



We have already noted, page 156, the frequent occurrence in 

 the cow of what is known as freemartins, or of twin pregnancy, 

 in which one of the pair of twins has become arrested in its sexual . 

 development and remains to some extent hermaphroditic, or 

 neutral, in character. 



The Diagnosis of Multiple Pregnancy in uniparous ani- 

 mals is seldom called for except in cases of difficult labor. Even 

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