SPERMATOGENESIS— INSEMINATION 171 



(p. 178), in which the male cells retain their vitality for long 

 periods, these must at such times remain quiescent, for otherwise 

 their store of energy would soon become exhausted. 



The spermatozoa swim by means of their tails. The movement 

 is represented in the accompanying figure (taken from ISTagel),! 

 which shows the successive positions assumed by the sperm in a 

 state of locomotion. A wave of movement first makes its appearance 

 in the forepart of the tail, and then rapidly travels backwards to 

 the end, to be succeeded by a fresh wave which follows the same 

 course. It would seem that the driving force is located a little' 

 behind the head. The head itself does not appear to be concerned 

 in the movements of locomotion. 



The movements of spermatozoa have probably been studied most 

 closely in Insecta and Echinodermata. BuUer^ says that the 

 sperms of the Echinoidea in a drop of sea-water (or the medium in 

 which they are normally discharged) swim spirally, so long as they 



Fig. 55. — Diagram illustrating wave-like movement of swimming 

 spermatozoon. (From Nagel.) 



do not come into contact with the surface. The spirals . may be so 

 steep that the sperms appear to move almost in a straight line, in 

 which case progression across the field of the microscope is relatively 

 rapid. In other cases the incline of the spiral is so slight that the 

 spermatozoa swim' almost in circles, and consequently move forward 

 across the microscopic field with great slowness. Every gradation 

 between these two extremes was observed but the more active 

 sperms generally swam in the steeper spirals. 



Dewitz ^ has shown that when the spermatozoa of the cockroach 

 are put into 0'6 per cent, solution of sodium chloride, and placed 

 between two surfaces, such as those of a slide and a cover-glass, they 

 collect after a short time, partly upon the upper surface of the slide 



1 Nagel, Randbuoh der Physiologie des Menschen, vol. ii., Braunschweig, 1906. 



2 Buller, "Is Ohemotaxis a Factor in the Fertilisation of the Eggs of 

 Animals?" Quar. Jour. Micr. Science, vol. xlvi., 1902. 



' Dewitz, "Ueber Gesetzmassigkeit in der Ortsveranderung der Sper- 

 matozoen, etc.," Pfluget's Archiv, vol. xxxviii., 1886. Rotation by spermatozoa 

 seems to have , been recorded first by Eimer, " Untersuchungen liber den 

 Bau und die Bewegung der Samenfaden," Verhand. d. Phys. Med. Oesel. zm 

 Wilrzhiirg, vol. vi., 1874. 



