164 Edmund B. Wilson 



viduals, owing to close union of the two idiochromosomes. But 

 in very many cells of this period the chromosome-nucleolus con- 

 sists of two very distinct unequal moieties, in contact (Fig. 6, a, 

 b, Photo 25), or not infrequently widely separated (Fig. 6, c, d. 

 Photo 26). When in contact they form a double body closely 

 similar to the idiochromosome-bivalent of the second division. 

 There can be no question of confusing either of these bodies with 

 the plasmosome, since the latter, showing its characteristic stain- 

 ing reactions, is also present. 



In the late prophases of the first division the idiochromosomes, 

 if previously united, almost invariably part company to divide as 

 separate univalents, as in other Hemiptera; but they usually 

 remain near together outside the principal ring. Only very excep- 

 tionally do they divide together. 



The spermatogonial groups (Fig. 4, m-q) uniformly show 22 

 chromosomes, and in some cases the small idiochromosome may 

 be recognized by its small size (/«, q). This is, however, not 

 nearly so marked as in the first division, since it now appears rela- 

 tively twice as large, owing to the univalent character of the other 

 chromosomes, and often it cannot certainly be distinguished from 

 the smaller of these {n, p). 



These facts make it clear that if the small idiochromosome be 

 supposed to disappear, the entire series of phenomena would be- 

 come identical with those shown in the 21-chromosome individuals, 

 the large idiochromosome now appearing as the odd or "acces- 

 sory" chromosome. 



The unreduced female groups of this type (ovarian cells) are 

 closely similar to those of the male (Fig. 4, r-t) but a small idio- 

 chromosome can never be distinguished. The absence of this 

 chromosome cannot be so convincingly shown in Metapodius as 

 in such forms as Lygaeus or Euschistus, owing to its greater rela- 

 tive size. Nevertheless, after the detailed study of many female 

 groups I am convinced that this chromosome is not present, and 

 that all the chromosomes may be equally paired. Apart from 

 analogy, therefore, I think the conclusion reasonably safe that 

 in Metapodius, as in other forms, the unequal idiochromosome- 

 pair of the male is represented in the female by a large equal pair, 



