92 PROBLEMS OF FERTILIZATION 



active in sea-water; but in the case of the starfish 

 they usually do not activate greatly in sea-water, 

 save in the presence of excess of OH ions or secretions 

 of the eggs of the same species, a matter to which we 

 shall return. In mammals the spermatozoa are active 

 in the ejaculate which contains secretion of the pros- 

 tate and other glands. Sperm taken from the epidid- 

 ymis will activate in physiological salt solution. 



Spermatozoa are probably incapable of receiving 

 nourishment outside of the gonad after they are fully 

 differentiated; certainly in the case of all forms with 

 external insemination there is no opportunity for the 

 restitution of substance. We must therefore regard 

 these cells as charged with their full available store of 

 energy in the testis and their capacity for locomotion 

 as thus determined and limited. They therefore have 

 a strictly limited period of life, the duration of which 

 will be determined by their activity. The store of 

 energy is saved when they are motionless and expended 

 when in motion. Thus we find that sperm suspensions 

 will retain their fertihzing power for a relatively long 

 time if activity is reduced, and will lose it relatively 

 rapidly if activity is great. Cohn (1918) has deter- 

 mined that the total CO2 production of spermatozoa 

 is the same whether their life be long or short. 



The amount of energy produced has not been meas- 

 ured, but it is necessary to describe it as surprisingly 

 large; a certain degree of motion may be kept up for 

 hours at a time. The source of the energy is certainly 

 in the cytoplasm, as the highly condensed nucleus is 

 in a condition which all cytological experience inter- 

 prets as a state of quiescence. If in the cytoplasm, 



