PHYSIOLOGY OF THE SPERMATOZOON 93 



the cytological data would suggest the mitochondria 

 as a source of energy. This is, however, purely specu- 

 lative, for the subject has not been studied from this 

 point of view; but the universal presence of mitochon- 

 dria in the sperm suggests some important function, and 

 they are almost certainly not heredity material. 



The locomotion of flagellated spermatozoa seems to 

 be essentially similar in all animals. The spermat- 

 ozoa of Nereis in their free movements through the 

 water describe spiral paths with rather close-set turns. 

 As soon as a spermatozoon comes in contact with a 

 surface it tends to move round and round in circles 

 in contact with the surface in anticlockwise direction; 

 the forward component of the locomotion is largely 

 eliminated under these conditions. The movement is 

 due to successive beats of the tail, and it is an interest- 

 ing fact that under certain conditions of aggregation 

 the successive beats of the aggregated spermatozoa 

 may become synchronous; the rate is about 120 a 

 minute at 20° C. under such circumstances (LiUie, 



1913)- 



The spermatozoa of sea urchins also swim spirally 



when freely suspended. "The spirals may be so steep 



that the spermatozoa appear to swim in ahiiost a 



straight line, and they then move relatively rapidly 



across the field of the microscope. On the other hand, 



the incline of the spiral may be so gentle that the 



spermatozoa appear to be swimming almost in circles" 



(Buller, 1902). The spermatozoa of sand dollars behave 



similarly. Ballowitz (1890) and Dewitz (1885, 1886) 



describe similar forms of behavior for various insects, 



Massart (1888, 1889) ^or Amphibia. 



