CORPORA ALBICANTIA, CORPORA ABERRANTIA AND CORPORA ATRETICA 



379 



7 8 9 IO II 12 13 



TOTAL NUMBER OF CORPORA 



Text-fig. 21. Changes in the mean number of 'old' (white circles) and recent ('young' and 'medium') 

 corpora albicantia (black circles), with increasing corpora numbers. 



40 



10 



20 30 40 



TOTAL NUMBER OF CORPORA 



50 



Text-fig. 22. Changes in the mean number of 'old' corpora albicantia with increasing corpora numbers. 



Two possible explanations of this rise in the number of recent corpora albicantia associated with 

 increasing age could be advanced. One is that there is a progressive human error in the counts, a 

 tendency to overestimate the number of recent corpora as the total number of corpora increases. This 

 can be checked and does not account for this large increase. 



Another explanation is that the rate of regression becomes progressively slower with age, the duration 

 of the ' young ' and ' medium ' stages being longer and the number of corpora in these stages increasing. 

 It is possible to apply a test to this hypothesis, because if the rate of regression is slower then the 



