574 THE POPULAR SCIENCE MONTHLY 



Menclelian inheritance. In the crossing of two individuals that re- 

 semble each other externally, progeny of many different kinds are 

 produced. In crossing white and cream-colored four o'clocks Correns 

 got eleven kinds of red, white, yellow and striped offspring among the 

 grandchildren. Heredity, as the Mendelian analysis has revealed it to 

 us, is a process of producing a great mmiber of diverse combinations by 

 the varied intermingling of the characteristics (concealed or apparent) 

 of two individuals. 



Now, it seems clear that this is exactly what is done in the conjuga- 

 tion of the infusoria. We have not 3'et succeeded in determining the 

 precise rules of recombination, such as have been worked out for many 

 cases in higher organisms; so that for the infusorian we are as yet 

 limited to the statement that conjugation produces variation. 



Thus the conjugants apparently have the same relation to each other, 

 so far as inheritance is concerned, as do sperm and egg in the higher 

 organisms. We ought to find that the progeny inherit from both of 

 the conjugants. What are the positively known facts as to this ? 



Eegarding biparental inheritance in these lower animals, we are as 

 yet in that relatively backward stage of science that is implied by the 

 necessity for the use of statistical methods. 



We hear at times the Kantian dictum that any subject is scientific 

 only to the extent that it makes use of mathematics. This dictum is 

 sometimes put before us as an argument for using statistical methods. 

 But for these we could almost reverse the statement, and say that any 

 subject is scientific only to the extent that it can dispense with statis- 

 tical methods. These are necessary mainly when we can not under- 

 stand and control the separate causes that are at work; as soon as we 

 can do this such methods become largely unnecessary. 



But the use of statistical methods enables us to show that in conju- 

 gation the progeny inherit from both parents. By working out for 

 the rate of fission the coefficient of correlation between the descendants 

 of the two that have conjugated, we find that they have nearly the same 

 closeness of relationship as brothers and sisters; and somewhat closer 

 than cousins. The coefficient of correlation is about .4. This means 

 that if the progeny of one member of a pair have a peculiarity, the 

 progeny of the other member have the same peculiarity, though in a less 

 degree, and this similarity can apparently come only through inherit- 

 ance from both parents. 



Comparing conjugation with the fertilization of higher animals, we 

 find then this state of the case. In higher animals fertilization has two 

 diverse effects, which recent investigation, particularly that of Loeb and 

 his associates, has clearly disentangled. (1) On the one hand, it 

 initiates development ; it prevents the egg from dying, as it would do 

 if not fertilized. This function of fertilization is the one that is 

 replaced by the processes which induce artificial parthenogenesis. 



