SEC. 2. THE MALE OKGANS. 



688. The tail of a spermatozoon may be regarded 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 ( 86) concern- 

 ing 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 sperma- 

 tozoon 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 movement 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 move- 

 ments may largely depend on the condition of the secretions in 

 the vagina and uterus. In this connection it may be noted that 



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