I04 SECTIONAL ADDRESSES 



little value. The fact that it is never equality is of course a matter of 

 considerable interest, and invites speculation, but unfortunately the figures 

 relating to pre-natal and early post-natal death are but few, and, for the 

 most part, were garnered many years ago. However, it is the case that 

 in all instances in which figures for the sex ratio of still-births amongst 

 these animals of the farm have been examined they always show that this 

 is higher than that amongst live births. Thus Goehlert (1888) gives 

 106 : 100 for still-births, and 96-5 : 100 for live births amongst horses. 

 In cattle, Lillie (1916) found the sex ratio amongst still-births to be 

 134 : 100 ; Jewell (1921) 123 : 100, that for live births being loo-iio : 100. 

 Parkes (1925), examining the sex ratio amongst pig foetuses classified 

 into different weight groups, found that the sex ratio was very much 

 higher amongst them than was the standard secondary sex ratio, and, 

 further, that the size groups showed an inverse correlation between male 

 percentage and the stage of development. He concluded that the primary 

 sex ratio in the pig must be about 160 : 100. Krizenecky (1935) in a 

 review of the sex ratio in the pig gives that of still-births as 119 : 100, 

 compared with loi -8 : 100 for live births. 



The figures for post-natal mortality from natural causes amongst these 

 animals are of course exceedingly rare, for it is man himself who here 

 wields the sickle. For this reason the tertiary sex ratio (that which 

 obtains amongst an adult population) provides no information of any 

 value to the present discussion. However, my colleagues have provided 

 me with figures which show the relative male and female wastage amongst 

 our pigs between birth and weaning. The secondary sex ratio amongst 

 2>336 pigs is 104-9 : 100, whereas that amongst the 1,489 which remain 

 alive at the time of weaning has fallen to 97-4 : 100, the percentage loss 

 amongst the males being 38-6, that amongst the females, 33-7. These 

 figures suggest that the pre-natal mortality in the pig which discriminates 

 against the male is continued at least up to the time of weaning. 



Thus, as far as they go, the figures relating to the mammals of the farm 

 without exception suggest that the male amongst them shares with the 

 male of man a relative frailty and endures a selective elimination both 

 before and after birth. 



The laboratory rat and mouse have provided records which, though 

 far less numerous, are more reliable than those derived from stud books. 

 The secondary sex ratio of the albino rat is accepted as being roughly 

 ic6 : 100, that amongst still-born rats was found by King (1921) to be 

 129-3 : 100. In the case of the mouse the secondary sex ratio for the 

 ordinary albino as recorded by different investigators is round about 

 equality with a slight suggestion of male excess. There is some difference 

 of opinion concerning the relation of pre-natal mortality and the secondary 

 sex ratio in this animal. The earlier observations of Parkes .(1924) 

 suggested that there was a considerable pre-natal mortality and that this 

 vi^as sexually selective, falling preponderatingly on the male. Contmua- 

 tion of this study, however, failed to support this conclusion. Further- 

 more, McDowell and Lord (1925), in the case of their own mouse stock, 

 have shown fairly conclusively that during gestation there had been no 

 continuous sexually selective elimination of one sex or the other. In the 



