56 BIOLOGICAL LECTURES. 



are alike, why is the second necessary ? why cannot one do 

 the work of both ? The apparent extravagance seems quite 

 justified, especially if we grant that the attraction sphere is 

 indeed an attraction sphere, an expression of force, and that it 

 is as necessary to the sperm as to the egg. If the sperm must 

 depend upon the egg's attraction sphere, it is apparently ham- 

 pered by at least two conditions : it must penetrate far enough 

 into the egg to be within ''working distance" of the egg 

 attraction sphere, and it must penetrate at the right time, that 

 is, while the egg attraction sphere is present. (In this egg, you 

 remember, and in many other forms, the egg attraction sphere 

 disappears at a definite time, that is, after the second polar body 

 has been formed.) If, however, the sperm has its own attrac- 

 tion sphere, it is not hampered by the above-mentioned condi- 

 tions as to space and time, and a study of the literature shows 

 that it does enter at very different stages of the development 

 of the egg, in some forms even while the germinal vesicle is 

 intact, and in many more forms as late as after the second polar 

 body is formed; if it enters too early, it simply waits at any 

 point in the egg for its attraction sphere (until the anaphase of 

 the first spindle) and if it enters late its attraction sphere 

 forms at once at the periphery. If these observations are of 

 any value, they suggest that the sperm is relatively independent 

 as to the exact time of its entrance and the distance it must 

 penetrate, and that thus the egg has a much better chance of 

 being fertilized ; it would be poor economy for it to save an 

 attraction sphere and lose a sperm. 



There seems to be at least one case in which the egg attrac- 

 tion sphere does do double work. Dr. Wheeler's work on 

 Myzostoma has shown us that at no time during fertilization 

 does an attraction sphere appear in connection with the sperm, 

 and it is interesting to note that this egg is fertilized very 

 early while the germinal vesicle is still intact. (The sper- 

 matozoon takes no risks of arriving too late to utilize the egg 

 attraction sphere.) Another observation of Dr. Wheeler's on 

 this form is extremely interesting: The spermatozoon has no 

 middle-piece a very significant circumstance (as Dr. Wheeler 

 says) in connection with the fact that there is no sperm attrac- 



