What is the Result of Mating 37 



What ground then can we possibly give for the inter- 

 change of parts of the two individuals that conjugate? We 

 shall take up this question in all its aspects later; here I 

 wish to bring up but one of the possibilities. We observe 

 that after the two individuals have conjugated and sep- 

 arated, they are no longer just what they were before. Each 

 is now formed of parts of two individuals, a body and half 

 the nucleus from one; half the nucleus from the other. 

 Will the two individuals therefore now be diverse in other 

 respects from what they were before? Will their general 

 characteristics be changed? Will they behave differently; 

 will they develop differently; will they produce young of a 

 different sort ? In other words, are the other characteristics 

 of the two individuals mixed as well as their nuclei? 



This we know is what happens as a result of fertilization 

 in higher organisms ; the young produced inherit from both 

 parents. Does it happen also in the Protozoa? If so, it 

 will give us an understanding of the exchange of parts in 

 mating. 



This raises for us the problem of heredity in the Protozoa. 

 Do the young produced by any given parent inherit also 

 from the individual with which that parent has mated? 



But this is heredity in its most complex form. In the 

 Protozoa, as we have seen, we have, for generation after 

 generation, reproduction from a single parent by simple 

 division. This presents the problem of heredity, and also 

 those of variation and evolution, in the simplest possible 

 form, and we shall do well to study the problems here 

 before we take them up in cases where two parents are 

 involved. We shall therefore examine this matter in our 

 next lecture, and later take up the entire natural history of 

 mating. 



