Recombinations of the Primary Hereditary Characters 185 



of chromosomes, with resulting formation of a new combina- 

 tion through mating. 



For the Protozoa it is clear therefore that so far as the 

 primary hereditary characters the chromosomes are con- 

 cerned, mating is a process of producing new combinations 

 of hereditary characters. In higher organisms we know 

 that these primary hereditary characters are what determine 

 also the later or secondary hereditary characters, those 

 that appear in the developed body. There can be no doubt 

 that the same is true of the Protozoa. Everything indicates 

 that in these respects mating in the Protozoa is the same 

 sort of thing that it is in higher organisms, and that when 

 the matter is fully studied it will be found to produce the 

 same kind of results. Mating may be defined as the process 

 of producing new groups of hereditary characters, primary 

 and secondary, by combining diverse half groups from dif- 

 ferent nuclei. 



But what shall be said from this point of view of the cases 

 in which the two half nuclei are produced from a single one, 

 and these two later unite in mating, as in the numerous cases 

 of autogamy (Figure 41, etc.)? These cases form a diffi- 

 culty for almost any other way of looking at the matter, but 

 not for this one. For new combinations of the primary 

 hereditary characters are formed likewise when the mating is 

 between two nuclei that are recent products of a single one. 



In all cases of such autogamy, a fact is observed which 

 becomes of the greatest significance. After a single nucleus 

 has divided into two, these two do not reunite at once, but 

 there are always one or two intervening divisions. And it 

 is these intervening divisions that bring about the reduction 

 in number of the chromosomal packets, with the consequent 

 formation of new combinations of the primary hereditary 



