504 JENNINGS— HEREDITY IN PROTOZOA. [April 24, 



will we obtain two diverse lines, one showing a greater mean size 

 than the other ? 



As we have already seen, our first attempts to do this failed. 

 But these first experiments were made before our study of growth and 

 environmental effects, so that the basis of selection was wrong. The 

 smaller specimens selected were as a rule the younger ones ; they 

 grew to full size, then, of course, pro^duced progeny of the same size 

 as other adults. 



After the thorough study of growth, it appeared possible that a 

 more adequate method of selection might be found. The propor- 

 tions of the young differ from those of the adult (as our account has 

 shown), so that after long practice one comes to recognize the young 

 specimens with some accuracy. It appeared worth while, therefore, 

 to attempt to select larger and smaller adults for further propagation. 



(a) Differences Due to Environmental Action Not Inherited. 



It is, of course, easy to obtain within a pure line adults of dift'er- 

 ent size, by subjecting them to different environments. An analysis 

 of our section on the effects of the environment shows that as a rule 

 these are not inherited. Thus, if we examine Table XVIII. (page 

 460), we find that the same set that gave on July 17 a mean length 

 of 184.100 microns (row 7) gave one week later, under different 

 conditions, a mean of 146.108 microns ; one day later 163.932 microns ; 

 one week later 174.400 microns; two days later 191.360 microns. 

 The breadth changed even more, and the extremes of size in a given 

 culture showed corresponding changes. There was no difficulty in 

 changing the dimensions back and forth in the most varied ways. 

 The entire Table XVIII. is an illustration of the general lack of 

 continued inheritance of environmental effects. 



Many experiments directed precisely on this point gave the same 

 results. When, for example, the small specimens of row 8 (Table 

 XVIII.) were cultivated under the same conditions as large speci- 

 mens from row 9, the resulting cultures were soon indistinguishable. 



Thus, it is clear that such environmental action as is summarized 

 in Table XVIII. is not as a rule inherited. But I wish to point out 

 and emphasize certain facts regarding the experiments on the action 

 of the environment, (i) In all the experiments thus far tried, the 



