720 THE PHYSIOLOGY OF REPRODUCTION 



Thus the nucleoli are often apparently quite absent in extreme old 

 age. The nuclei, besides becoming smaller, grow irregular in shape, 

 and in the cytoplasm there is a deposition of pigment granules. 



Senescence in men is said to commence at about the age of fifty, 1 

 but it is obvious that no definite limit can be assigned to the period, 

 since in some of the organs changes which are in their nature 

 degenerative begin quite early in life. 



Spermatozoa continue to be produced even in quite advanced old 

 age, and instances have been recorded of men of 94, 96, and even 103 in 



c^^^^K^^f' ' ' Iff/ 

 /IlK :$Mdm. ^n^ 



FIG. 187. Group of nerve-cells from the first cervical ganglion of a man of 

 ninety-two. (After Hodge, from Minot's Age, Growth, and Death, 

 G. S. Putnam & Sons, and John Murray.) 



C, C, Cells still intact, but shrunken and loaded with pigment ; 

 c, c, cells which have disintegrated. 



whose semen active sperms were found. 2 There can be no doubt, 

 however, that the spermatozoa are produced in far less abundance in 

 old age. 



In women the period of senescence is usually reckoned from the 

 menopause. 3 



It is difficult to form any accurate comparison between the 

 phases of life of men and those of animals, partly because so little is 

 known regarding the conditions of natural senescence and death in 



1 Lee, loc. cit. 



2 Cooper, The Sexual Disabilities of Man, etc., London, 1908. 



3 For further information bearing on the subject see Stanley Hall, Senescence, 

 New York, 1922. 



