ORTHOPTERAN SPERMATOGENESIS 653 



that its organization is very precise and that the most tangible 

 evidence of this is its method of integration into a definite and 

 characteristic series of units in each kind of organism. 



From many careful studies of a great number of different ani- 

 mals and plants the following facts have been determined beyond 

 any reasonable doubt: 1. In both male and female — with a 

 significant exception — there occur identical and duplicate series 

 of these chromatin units. 2. During maturation this duplicate 

 series is reduced in number to one-half by the joining of homol- 

 ogous pairs together. 3. In the course of the two maturation 

 mitoses these paired elements are disjoined with the final result 

 that each mature germ cell is provided with one representative 

 of each pair. 4. When the paternal and maternal germ cells 

 thus produced come together in fertilization there is restored 

 again the duplicate series with which the process started. 



There is nothing to indicate that any other parts of the cell 

 have such significance as the behavior of these chromatin units 

 indicates is theirs, and accordingly the phenomena of their junc- 

 tion and disjunction requires the most exact analysis. There are 

 many complicated changes taking place here, and the condi- 

 tions are such as to make it difficult, or even impossible in some 

 cases, to determine exactly what are the facts. Each step in 

 the process must however be understood and no effort should be 

 spared to ascertain" all the facts. Of the greatest importance 

 are the stages immediately following the last division with the 

 unreduced number of chromosomes. At this time, undoubtedly, 

 changes of vital significance occur, but unfortunately they are 

 very involved and difficult to determine in detail. However, one 

 fact, which is the important one in connection with the present 

 study, stands out clearly: the series of chromosomes present 

 in the last mitosis with the unreduced number reappears in easily 

 recognizable form in the prophase of the first maturation division. 

 The only difference of importance is that instead of being present 

 in a series of single elements, the chromosomes are now joined 

 together in pairs so that the number of independent chromatin 

 bodies is one-half of that in the preceding generation. But noth- 



