94 PROBLEMS OF FERTILIZATION 



The conditions under which spermatozoa are usu- 

 ally observed are not favorable for observation of 

 unimpeded locomotion; the material is usually observed 

 in the form of suspensions of greater or less density in 

 which the individual spermatozoa are continually collid- 

 ing with one another and with the walls of the chamber 

 in which they are confined. Under such circumstances 

 the distribution of active spermatozoa should be uni- 

 form, like the molecules of a gas, and this condition is 

 found in perfectly fresh suspensions. However, it 

 usually does not last long and various forms of aggre- 

 gation result. 



The spermatozoa of Nereis suspended in sea-water 

 give a very striking reaction which illustrates the point. 

 If a drop of dry sperm from a mature Nereis is mixed 

 in about 6 c.c. of sea-water in a Syracuse watch crys- 

 tal it makes a uniformly milky suspension; in a few 

 seconds clouds begin to appear, and in fifteen to forty- 

 five seconds these usually draw together in white solid- 

 looking masses uniformly spaced through the fluid 

 (Fig. 13). The intervening fluid becomes quite clear 

 and the masses quickly settle on the bottom. The 

 rate of formation of these masses and their number and 

 size depend on condition of the animal furnishing the 

 sperm, temperature, ''freshness" of the sperm, reaction 

 of the medium, etc. Sperm suspensions of most animals 

 do not, however, exhibit such marked aggregations. 



III. BEHAVIOR OF SPERMATOZOA 



The function of the spermatozoon is apparently 

 bound up with its capacity for locomotion; it is prob- 

 able that immobilized sperm will not fertilize, in 



