274 



Mr Punnett, 



the sex and condition of birth (i.e. alive or dead) of the infants 

 are known. From these data have been constructed the curves 

 shewn in Fig. 1. The absolute number of g births was used 



Fig. 1. 



13 15 17 19 21 23 25 27 29 31 



14 16 18 20 22 24 26 28 30 32 



33 35 37 39 41 43 45 47 



34 36 38 40 42 44 46 



Age of Mother. 

 <? curve represented by continuous, ? curve by broken line. 



whilst the % births were brought up to a comparable level by 



total g births / 3625 



multiplying by the fraction ^ % ^^ 



in this case 



)• 



3313 



The resultant curve indicates the relative number of % births 

 compared with the number of £ births at different ages of the 

 mother. The noteworthy features of the curves are (1) the 

 equality up to the age of 19, (2) the relative preponderance of % 

 births in mothers of 19 — 23, followed by (3) a relative prepon- 

 derance of <f births. The differences are not very great, and if 

 supported by this material alone might be objected to as acci- 

 dental. I have therefore constructed curves in the same manner 

 from the only other similar data known to me, viz. that given by 

 Diising 1 for two groups of first births containing respectively 4441 

 and 5756 cases. The resultant curves (Figs. 2 and 3) bear a 

 close resemblance to Fig. 1 in the three points mentioned above. 

 1 loc. cit. The data for Fig. 2 are given on p. 604, those for Fig. 3 on p. 605. 



