MULTIPAROUS FEMALES 455 



The appearance of the corpora lutea in the case where there were four simultaneous ovulations is 

 illustrated in Text-fig. 10 a. The female which had 13 corpora lutea in the ovaries was examined by 

 Dr R. H. Clarke on 25 February 1948 in 6i° 14' S., 87 25' E., and measured 78-5 ft. in length. This 

 female carried 5 male foetuses of lengths 2-03, 2-26, 2-28, 2-54, and 2-67 m., the first of which was 

 necrotic, the others healthy. There were 16 corpora albicantia in the ovaries and details of the 

 13 corpora lutea are given in Table 27. It will be seen that none of the corpora lutea is of very 

 small size, ranging from 7 to 14-5 cm. in diameter, and all would therefore be expected to leave a 

 permanent record in the ovaries (p. 375). 



Making due allowance for these supernumerary corpora lutea it is estimated that on average 

 1 -034 corpora lutea are formed each ovulatory cycle, that is to say the proportion of extra ovulations is 

 3 -4 ±1-02%. With a smaller sample (part of the present sample) in which the corpora lutea were 

 examined in detail the proportion of accessory corpora lutea was 3*7% (p. 361). 



Proportion of females in oestrus or pregnancy 

 Another aspect of the variation in sexual activity with age can be studied by examining, for successive 

 groups of corpora numbers, the percentage of adult females which show one or more active corpora 

 lutea in the ovaries. The majority of these females will be pregnant, but a small proportion are in a 



100 



b 



z 

 u 



2 50 

 s 



NUMBER IN SAMPLE 

 776 416 268 192 116 67 42 20 3 2 5 



100 



NUMBER IN SAMPLE 

 490 281 178 128 76 49 29 IS 3 2 I 



A 1 h 



O 5 10 15 20 25 30 35 40 45 50 55 

 NUMBER OF CORPORA 



O 5 10 15 20 2 5 30 35 40 45 50 55 

 NUMBER OF CORPORA 



b 



Text-fig. 52. a, Percentage of mature females which have an active corpus luteum in the ovaries. 

 b, Percentage of these corpora lutea which represent pregnancies. 



post-oestrus condition following a recent unsuccessful ovulation (p. 437). Owing to differential 

 migration, mortality, etc., the figures obtained will not exactly represent the true proportion of females 

 which are still experiencing oestrous cycles, but will give a picture of the relative variation in activity 

 with age. 



The results are shown in Text-fig. 52 a, in which data on 1907 mature females examined between 

 1925 and 1954 are utilized. For successive age groups (expressed as corpora numbers) the percentages 

 of mature females with corpora lutea are shown. The vertical range represents the percentages ± 2 S.E., 

 and the results for the last three groups have been combined so as to increase the size of the sample. 



Over this range of ages the percentage frequency of pregnancy or post-oestrus stages does not vary 

 significantly, but taking the figures as a whole it would seem that fertility increases very slightly up to 

 an age corresponding to 40-50 corpora (estimated to be about 35-40 years; see pp. 465-66), after 

 which it may decline. 



A proportion of these females have ovulated recently without becoming pregnant, and it is, there- 

 fore, interesting to see whether the percentage of unsuccessful ovulations varies with age. There are 

 1252 females in the material which have corpora lutea in the ovaries, and these are again divided into 

 successive age groups according to corpora number. For each age group the proportion known to be 

 pregnant, because a foetus was noted, has been calculated. Some few pregnant females in which the 

 17 DL 



