368 THE TESTIS. [BOOK iv. 



purpose, or being eventually disintegrated may be lost among the 

 more fluid parts of the semen which serve as a nutritive and 

 mechanical vehicle for the spermatozoa, or may pass bodily into 

 the secretion as undifferentiated nucleated cells. 



It may well be imagined that the transformations needed for 

 the development of the potent spermatozoa are of a special kind, 

 ami that the changes within the seminal tubule are in more 

 ways than one unlike those taking place in an ordinary epithelium ; 

 but concerning the details of the changes there is at present great 

 diversity of opinion. The important fact for our present purposes 

 is that in the seminal tubules spermatozoa are developed out of 

 some or other of the lining epithelium cells, and further are 

 developed in such a way that a specialized nucleus becomes the 

 head, while the body (middle piece) and tail appear to be of 

 the nature of cell-substance. 



942. The tail of a spermatozoon may be regarded, as we 

 have said, as a single cilium, the movements of which are of 

 an undulatory character, the waves travelling from the middle 

 piece to the end of the tail.; and the statements previously 

 made ( 94) concerning ciliary action may be applied generally 

 to the movement of a spermatozoon. The motion is apparently 

 not a very rapid one, for it has been calculated that a half 

 vibration takes at least a quarter of a second. It has also been 

 calculated that a spermatozoon progresses at the rate of about 

 2 or 3 mm. a minute. 



When discharged semen is left to itself the movements continue 

 for some (24 or 48) hours, but they appear to last much longer in 

 the female passages. Spermatozoa have been observed in move- 

 ment when removed from the neck of the living human uterus 

 5 or even 7 days after coitus ; and in some of the lower animals 

 the duration of vitality may be enormously long. Making all 

 allowance for any possible direct nutrition of the living substance 

 of the spermatozoon by means of the fluid of the semen, we must 

 conclude that the energy of the movement is derived from the 

 expenditure of what we may venture to call the contractile 

 material stored up in the middle piece and tail of the organism 

 at its formation ; the material of the head we may suppose to be 

 devoted entirely to the work of impregnation. So small a store 

 must be soon exhausted ; hence it is difficult to suppose that 

 vigorous movements can be continued for very long periods ; and 

 probably the activity of the spermatozoa is largely dependent on 

 the circumstances by which it is surrounded ; it may remain 

 motionless in one medium, and become active when the medium 

 is changed. The spermatozoon is probably quiescent so long as it 

 remains in the seminal tubes, but we have no exact information as 

 to whether or no movements begin in the epididymis and vas 

 deferens without exposure to air; and it is possible that after 

 coitus the beginning and maintenance of its vigorous movements 



