412 RUTH J. STOCKING 



VI. THE ABNORMALITIES AS HEREDITARY CHARACTERS; 

 VARIATION, INHERITANCE, AND SELECTION 



As we have seen, the abnormahties which we are considering 

 arise in consequence of conjugation. If half of a given stock 

 are allowed to conjugate, the other half not, the former develops 

 many of these abnormal races, while the latter develops none. 

 This shows that the abnormalities cannot be considered due to 

 infection, nor their reappearance in the stocks to the handing 

 on of an infecting organism. 



Since some lines are quite without abnormalities, while in 

 others, under the same conditions, the abnormalities reappear 

 for generations, it is clear that the tendency to abnormality is 

 inherited. That is, the difference between a stock that thus 

 produces abnormal individuals and one that does not, lies in the 

 constitutions of the stocks themselves, and is something that is 

 transmitted during vegetative reproduction. 



Such hereditary diversities occur not only between normal 

 and abnormal stocks, but also among the abnormal stocks them- 

 selves. Precise types of abnormality are indeed not inherited 

 exactly from parent to progeny; within a given line as we have 

 seen there is great variation as to whether abnormality appears 

 at all in a given individual, and as to the precise kind that occurs 

 when the individual is abnormal. Nevertheless, as before set 

 forth, certain types of abnormality are particularly common in 

 some lines, other types in other lines. The diverse lines differ 

 hereditarily in respect to something of which the diverse typical 

 abnormalities are the outward results. It is only by keeping 

 in mind the characteristic differences between lines that we shall 

 be able to grasp their relation to the problems of heredity. 



The hereditary diversities thus far mentioned are between 

 lines derived from diverse exconjugants. If anything like Men- 

 delian inlieritance occurs in infusoria, we could well expect such 

 lines to show hereditary differences; this is of course as a rule 

 true in any organism after the union of two parents to produce 

 progeny. 



On the other hand, in vegetative reproduction, and in general 

 in long continued uniparental reproduction of any sort, a remark- 



