CORPORA ALBICANTIA, CORPORA ABERRANTIA AND CORPORA ATRETICA 369 



finally lose their lumen and become solid cords of connective tissue. There is some evidence 

 that the external diameter of the arterioles may also increase with age. The average diameter of 

 10 arterioles in the single corpus luteum examined is 95-3 //, for 147 arterioles from 'young' and 

 ' medium ' albicantia it is 109 ft, and for 1 1 1 arterioles from ' old ' corpora it is 130 fi. This difference is 

 not, however, statistically significant. 



The relative thickness of the vessel wall seems to be a better quantitative index of the age of the 

 corpus than the diameter of the corpus and in general there appears to be less overlap between the two 

 groups of corpora albicantia in respect of this character. It would be interesting, though laborious, 

 to determine the relative thickness of the arteriole 

 walls for a complete series of say thirty corpora albicantia 

 from one pair of ovaries so as to gain some idea of the 

 variation in corpus size within a single animal. Since 

 for corpora albicantia of similar age, those formed from 

 corpora lutea of ovulation will be smaller than corpora 

 albicantia of pregnancy, it might perhaps be possible 

 to identify corpora of these two origins and to place 

 them in a chronological series. It might also be possible 

 in this way to establish the relative frequency of corpora 

 lutea of pregnancy and ovulation. This is the only 

 possible means of distinguishing corpora albicantia of 

 pregnancy from corpora of ovulation which is suggested 

 by the present study. It depends on the assumption 

 that although there is a large variation in corpus luteum 

 size in the whole population, for a single female it 

 might be expected that the size variation in corpora 

 lutea of these two origins would be slight. 



5 

 u 



a 



UJ 



\- 

 uj 



< 

 a 



a. 



a 

 O 

 U 



IO 



20 30 40 50 60 70 SO 90 



ARTERIOLE WALL AS°/ OF TOTAL DIAMETER 



ICO 



Text-fig. 15. Relation between size of corpus and 

 thickness of arteriole walls (corpus luteum — triangle ; 

 'young' and 'medium' corpora albicantia — open 

 circles, 'old' corpora albicantia — black circles). 



Persistence of corpora albicantia 

 In the routine examination of the 1955/56 ovary 

 collection 4065 corpora albicantia were classified into 

 these three stages of regression — 'young', 'medium' 

 and ' old ' — on the basis of their macroscopic appearance in the 5 mm. slices. The main criteria used 

 are the relative amounts of white connective tissue and brown ' luteal ' tissue. These types represent 

 stages in a continuous process so there is no definite line of demarcation between corpora in each of 

 the groups and it is sometimes difficult to decide in which of two groups a corpus should be placed. 

 This applies more to distinguishing ' young ' from ' medium ' corpora than ' medium ' from ' old '. In a 

 large sample these marginal corpora may be expected to cancel each other out. In addition to the 

 author, two colleagues (Mr A. E. Fisher and Mr J. H. Smoughton) have independently undertaken 

 the examination of parts of the material, and the fact that the results are consistent although obtained 

 by three separate workers supports the validity of the classification. 



In Text-fig. 16 the frequency distribution of mean diameters of these three types is presented. There 

 is an extensive overlap between all three groups; the size range for 'young' corpora is 1-5-7-5 cm., 

 for 'medium' corpora 0-7-5-5 cm., and for 'old' corpora 0-7-5-0 cm. The mean values and two 

 standard errors are 4-01 ±0-07, 2-94 ±0-05 and 2-01 ±0-03 cm., respectively. The frequency distribu- 

 tion for each group is as symmetrical as for the corpus luteum size frequency (Text-fig. 7). 

 The youngest corpora albicantia are most variable, both because the sample is smaller and because 



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