392 Experimental Zoology 
more girls are born. Other writers have published statistics 
that give exactly contrary results. Geddes and Thomson give 
such data in the following table : — 
FATHER 
FATHER YOuNGER 
AVERAGE 
OLDER THAN 
FATHER PROPORTION 
No. oF Propr, ‘i MoTHER 
OBSERVER Biers Loca.ity Mins SAME AGE Propr. or MALES 
AS MOTHER TO 100 
TO 100 MALEs F 
EMALES 
FEMALES TO 100 
FEMALES 
Hofacker 1,996 | Tiibingen 117.80 92.00 90.60 | 107.50 
Sadler 2,008 | England 121.40 94.80 86.50 | 114.70 
Gohlert 4,584 108.02 93-30 82.60 | 105.30 
Legoyt 52,311 | Paris 104.49 | 102.14 | 97.50 | 102.97 
Boulanger 6,006 | Calais 109.98 | 107.92 | 101.63 | 107.90 
Noivot 4,000 | Dijon 99.70 116,00 | 103.50 
Breslau 8,084 | Zurich 103.90 | 103.10 | 117.60 | 106,60 
Stieda 100,590 | Alsace-Lor- | 105.03 108.39 | 106.27 
raine 
Berner 267,946 | Sweden 104.61 | 106.23 | 107.45 | 106.00 
It will be seen that while three other statisticians obtained the 
same kind of results as did Hofacker and Sadler, two others 
give exactly opposite results. Contradictory evidence has also . 
been given for horses and sheep. As Schultze points out, the 
results may mean, if they mean anything, that the conditions 
do not determine the production of one sex or the other, but the 
survival of an excess of one or the other kind of egg. Bidder 
has shown in the case of women under 18 years of age bearing 
children that there is an excess of boys in the proportion of 133.9 
‘boys to 100 girls. 
Schultze tried to test this problem experimentally. Sexually 
immature female mice were placed with males of the same age, 
so that at the first period of heat conception might occur. The 
females at this time were between 10 and 15 weeks old. There 
were produced in all 60 males and 65 females. In other cases 
the females were isolated and first allowed to breed after the 
