132 Life and Death, Heredity and Evolution 



unite with the "female" half nucleus of the other individual. 

 The "female" half nucleus is a little larger; it simply re- 

 mains quiet, finally uniting with the "male" half nucleus which 

 migrates to it. 



The problem of sex comes, in perhaps its sharpest form 

 in the question: What makes the two "male" half nuclei 

 refuse to unite when they come in contact, while the "male" 

 and "female" do unite? 



One answer to all these questions is that given by Maupas 

 (1889). According to this, there is no physiological differ- 

 ence between the two half nuclei ; their difference of behavior 

 is a mere result of their accidental difference of position. 

 The migratory half does not move through any peculiarity 

 of its own ; the fact is merely that the half nearest the surface 

 of separation is seized by the movements of the surrounding 

 cytoplasm and carried over into the other mate. The fact 

 that the two migratory halves do not unite is again merely 

 due to their being pulled along by the cytoplasm. Save 

 for this activity of the cytoplasm, the two migratory half 

 nuclei could just as well unite with each other as with the 

 inactive half nuclei. According to this way of looking at 

 the matter, there is no sex difference between these two 

 half nuclei; indeed, sex has no meaning, save as a name 

 for certain external peculiarities. 



This is one possible opinion on the matter ; it rests upon, 

 or results in, the general view that there is no general 

 underlying peculiarity that constitutes sex diversity; and 

 that sexuality is not a general characteristic of living things. 



The other possible view is that the difference in appearance 

 and behavior of the two half-nuclei is a consequence of an 

 underlying physiological difference that makes sex. In sup- 

 port of this view there are urged certain facts observed by a 

 number of later investigators. One is that it is not true 



