96 PROBLEMS OF FERTILIZATION 



But motility is not the exclusive requirement; 

 the spermatozoon must exhibit other definite forms of 

 behavior with reference to the egg. It has, however, 

 proved impossible to analyze the behavior of the sper- 

 matozoon by direct observation of fertilization. Hence 

 it is desirable to observe the various forms of behavior 

 of spermatozoa apart from the egg in the expectation 

 of being able to utilize the information thus gained in 

 the study of fertilization. 



Spermatozoa are highly specialized cells with ref- 

 erence to behavior as well as to structure and function. 

 Their principal behavior reactions appear to be with 

 reference to temperature, contact, and chemical stimuli. 

 They are, indeed, like all cells, also sensitive to changes in 

 osmotic pressure; but we have no evidence of reaction to 

 light or gravitation. Their behavior consists in changes 

 in rate of activity, in maintaining contact with surfaces 

 either at rest or not, in alterations in direction of loco- 

 motion, and in adhesion to one another or other surfaces. 



I. Light, Gravity, Osmosis, Temperature 



By way of clearing the ground we may first consider 

 the least known, or least effective, possible sources of 

 stimulation. 



a) Light. — So far as known, animal spermatozoa are 

 quite indifferent to light conditions. The chlorophyll- 

 bearing spermatozoa of many plants, however, exhibit 

 definite responses to illumination. These are entirely 

 lacking in animals, but we cannot suppose that the 

 metabolism remains the same under all light conditions, 

 and no doubt careful investigation would show some 

 effect of presence or absence of light or of rays of differ- 

 ent length on the activity of spermatozoa. 



