78 Life and Death, Heredity and Evolution 



organisms. None of them can be applied directly to Dif- 

 flugia, since here we have uniparental reproduction, and most 

 of these schemes depend upon the mixing of two stocks. But 

 other schemes can be devised, which might apply to Dif- 

 flugia; we shall mention some of these. At present I wish 

 to ask your patience for a few moments for a closer analysis 

 of just what has happened in such a case as this. Such an 

 analysis will bring out the main questions and difficulties 

 that can be raised. 



What then is it that has actually occurred in such a case? 

 We began with a single individual; it consisted of a shell 

 filled with a mass of protoplasm, containing one or more 

 nuclear bodies. This mass had behaved in such a way as to 

 produce a shell of definite size, form, number of spines, and 

 the like. We found that when this mass of protoplasm gives 

 off one-half of itself to the outside of the old shell, this half 

 is made up, chemically or otherwise, in the same way 

 as was the original parent mass; for it does just the same 

 things that the parent mass did. That is, it produces a 

 shell essentiailly like that of the parent, of a similar size, 

 shape, number of spines, and the like (see Figure 12). This 

 is particularly striking when we compare this individual with 

 others of different race, or of different species, as in Figure 

 20 ; it is extraordinary to see these tiny masses of proto- 

 plasm, each conducting itself in a manner different from any 

 other ; each holding true to type. There must be very defi- 

 nite, and at the same time very delicate, chemical differences 

 between them. 



But as we follow for a long time our original individual 

 and its progeny, we find that the chemical nature of the 

 protoplasm very gradually changes as divisions occur, for 

 the behavior begins to slightly change. Although all under 

 the same conditions, some of the masses commence to produce 



