386 Edmund B. Wilson. 



twelve of the larger chromosomes unite to form the six peripheral 

 bivalents of the first division, that the thirteenth is the larger 

 idiochromosome and the fourteenth (the microchromosome) the 

 small idiochromosome. These two alone remain separate in the 

 first division as univalent chromosomes, thus giving a group of 

 eight instead of seven. This conclusion is in accordance with 

 Montgomery's interpretation of the facts observed by him in 

 Euchistus tristigmus, as pointed out beyond, except that he 

 believed that in this form the first division might in many cases 

 show only seven chromosomes, the "chromatin nucleoli" having, 

 like the other chromosomes, already conjugated to form a bivalent 

 body. My interpretation is strikingly confirmed by the facts 

 observed in Nezara; for in this case, where the first spermatocyte- 

 division shows two chromosomes of equal size and the smallest of 

 the group, the spermatogoma correspondingly show two equal 

 microchromosomes, as in Anasa, Alydus, or Protenor (Fig. 4^, /?). 

 Since these two are represented in the second division by a single 

 symmetrical dyad, which is again the smallest of the group 

 (Fig. 4 gf) it is evident that the two equal microchromosomes 

 must conjugate after the first division. They therefore agree in 

 behavior with the unequal idiochromosomes present in the other 

 forms, and differ from those of the Anasa type, in remaining 

 separate during the first maturation-mitosis. 



?. The Growth-Period of the Primary Spermatocytes. 



(a) General History. 



It is not my purpose to describe in detail at this time the general 

 history of the chromatin during the growth-period, but it will be 

 convenient to outline the stages in order to trace the history of the 

 idiochromosomes. In Lygaeus ten well marked stages may be 

 distinguished from the early synapsis (a) to the metaphase of the 

 first division (/), inclusive. Though some of these stages are best 

 characterized by the condition of the idiochromosomes, an account 

 of the latter can more readily be given after considering the history 

 of the larger chromosomes. In stage a (early synapsis), which 

 shortly follows the final anaphase of the last spermatogonial 

 division, the chromosomes have the form of rather ragged, longi- 

 tudinally split loops, the free ends of which converge toward 



