No. 510] HEREDITY AND VARIATION 



M2o 



with crystallization forces itself on us. The character- 

 istic form of crystals is easily changed ; by filing off the 

 angles we might convert a large number of pyramidal 

 crystals into the quite new form of cubes. But if we 

 dissolve these and allow them to recrystallize, we obtain, 

 not cubes, like the parents, but the original crystalline 

 form characteristic for that particular chemical com- 

 pound. 



If we should modify the chemical constitution of the 

 substance, it would then crystallize in new shapes. If 

 we could modify the fundamental constitution of the 

 organism we should probably find it likewise appearing 

 in new forms. Whether this occurs at times in uni- 

 cellular organisms we shall ask later. But it is im- 

 portant to grasp the fact that it does not occur often nor 

 easily; that the ordinary activities of life do not ob- 

 servably bring it about ; that the mere presence of a new 

 character in the parent has no evident tendency to pro- 

 duce such a result. Many of the untypical forms found 

 in Paramecium were such as one might imagine due to 

 an alteration in the fundamental constitution of the race 

 (a mutation?), but the new characteristic was not repro- 

 duced in the progeny. 



But besides the untypical or " abnormal" characters of 

 certain individuals, there are the common differences 

 among individuals that are fully "normal." In the Pro- 

 tozoa, as in all organisms, differences in size and propor- 

 tion among differing individuals are common; variation 

 is the rule here as everywhere. We must then examine 

 these differences, under the question already set forth: 

 What characters are produced anew in reproduction? 

 Will the progeny produce anew these diversities of the 

 parents, in such a way that from large parents arise large 

 progeny, from small parents small progeny, from inter- 

 mediate parents intermediate progeny! 



In Paramecium we find individuals differing greatly in 

 size. From a "wild" lot of Paramecia we isolate such 

 differing individuals and propagate from them, all under 



