82 EDMUND B. WILSON 



bivalents of the two in the second division. 4 The two species 

 may in fact readily be distinguished by mere inspection of the 

 chromatic nucleolus at this period. Already at this time the two 

 components are here and there seen to be separating, but as a 

 rule they do not finally move apart until the nuclear wall has 

 dissolved. From this time forward they cannot be individually 

 identified with exception of the small idiochromosome of N. 

 viridula, which is obvious at every period. 



As far as my material shows, the earlier stages of the idio- 

 chromosomes can not be so readily traced in Nezara as in some 

 other species, and the chromatic nucleolus can not actually be fol- 

 lowed backward to the spermatogonial telophases as can be 

 done in such forms as Lygaeus or Oncopeltus, of which a detailed 

 account will be given in a later publication. The prophase -figures, 

 however, decisively establish its identity with an unequal pair of 

 chromosomes that divide separately in the first spermatocyte- 

 division; and in N. viridula, one of these is certainly the small 

 idiochromosome. It may therefore confidently be concluded 

 that the chromatic nucleolus is identical with the idiochromo- 

 some-pair, as in so many other cases. Comparison of the division- 

 figures proves that this pair can not be identical with the small 

 pair that I formerly supposed to be the idiochromosome-pair; 

 and this small pair is moreover usually recognizable in the pro- 

 phase groups (s, in 5 y, z) in addition to the unequal pair. 



The foregoing facts make it clear that in Nezara the idiochromo- 

 somes undergo a process of synapsis at the same time with the 

 other chromosome-pairs, and that their separation before the first 

 division is a secondary process, to be followed by a second conju- 

 gation after this division is completed. A similar process often 

 takes place in many other Hemiptera. There are, however, some 

 forms, like Oncopeltus, in which the idiochromosomes are always 

 separate, from the last spermatogonial division through all the suc- 

 ceeding stages up to the end of the first division. In this case, 

 which I shall describe more fully hereafter, there can be no doubt 

 that the conjugation which follows the first division is a primary 

 synapsis, to be immediately followed by a disjunction. 



4 Cf. the earlier figures of the corresponding tetrad in Brochymena in my first 

 'Study,' fig. 7. 



