THE MALE ORGANS OF GENERATION. 



593 



FIG. 166. 



sufficiently moistened and at its normal temperature, the numberless 

 filaments with which it is crowded are seen to be in incessant motion. 

 In many species of animals, the 

 movement of the spermatozoa 

 strongly resembles that of a 

 tadpole ; particularly in the 

 mammalia, where they consist 

 of a short, well-defined head, 

 with a long and slender tail. 

 The tail-like filament is in con- 

 stant lateral vibration, by 

 which the spermatozoon is 

 driven from place to place in 

 the surrounding fluid, as a fish 

 or a tadpole is propelled 

 through the water. In other 

 instances, as in. the Triton, or 

 water-lizard, the spermatozoa 

 have a writhing or spiral-like 

 movement ; presenting a pecu- 

 liarly striking appearance when 

 large numbers are viewed to- 

 gether. 



Notwithstanding the energy 

 and rapidity of this movement, 

 and its resemblance in mechan- 

 ism to animal locomotion, it has 



no analogy with a voluntary SPERMATOZOA. a. Human, b. Of the rat. c. Of 



Meiiobranchus. Magnified 480 times. 



act. 



The spermatozoa are organic forms, produced in the testicles, and 

 constituting at first a part of their tissue. Like the egg, the sperma- 

 tozoon is destined to be discharged from the organ where it grew, re- 

 taining for a time its vital properties. One of these properties is its 

 power of movement ; but this does not indicate the possession of in- 

 dependent vitality, and is not even a proof of its animal origin. The 

 movement of a spermatozoon is not more active than that of a bac- 

 terium cell, or of the ciliated zoospores of certain fresh-water algaB. 

 It is analogous to the motion of a ciliated epithelium cell detached 

 from its mucous membrane, which will sometimes continue for many 

 hours, under favorable conditions of temperature and moisture. The 

 movement of the spermatozoa continues for a time after their separa- 

 tion from the body ; but it is limited in duration, and after a certain 

 interval comes to an end. 



In order to preserve their vitality, the spermatozoa must be kept at 

 or near the normal temperature of the body, and protected from the 

 contact of air or other unnatural fluids. If the spermatic fluid be 

 allowed to dry, or if it be diluted with water, in the case of birds and 



2X 



