172 



MONTGOMEBY A STUDY OK Til 10 (ill KOMOSOM I OS 



be seen on lateral view, one chromosome is always found to be of about half the size of 

 the others and not dumbbell-shaped ; on pole views this chromosome can be distin- 

 guished by its lesser depth. 



So in Alydus eurinus there is an uneven number of chromosomes in the spermato- 

 gonia, namely, eleven ; the reduction in number is effected then in the synapsis by ten 

 combining to form five bivalent ones, while one remains univalent and uncombincd. 

 because there is no mate with which it can unite. 



In the monaster of the second maturation division there are either six or seven 

 chromatin elements. In Fig. 100 of this stage arc shown seven, of which the smallest is 

 probably the chromatin nucleolus, five are halves of the originally bivalent chromosomes 

 and one probably the half of the originally univalent chromosome. 



In the spermatid we find either six. (Fig. 102) or five (Fig. 101) chromatin elements 

 of approximately equal volume. Now these elements are too large to be derivatives of 

 the chromatin nucleolus of the spermatocyte of the first order (iV. 2, Fig. 98), so that the 

 five or six elements of the spermatids would not seem to represent portions of this chro- 

 matin nucleolus ; very probably the latter is so small in the spermatids or generally so 

 closely applied to the surface of one of the chromosomes that it escapes observation. If 

 we then eliminate the possibility of any of the elements shown in the spermatids (Figs. 

 101, 102) representing chromatin nucleoli or their derivatives, then we must conclude that 

 the five or six elements here are chromosomes. But why is their number sometimes five, 

 in other cases six ? Now we know that in all other Hemiptera in which attention has 

 been given to this point that each spermatid receives one-quarter of each of the bivalent 

 chromosomes present in the spermatocyte of the first order. Accordingly it would be 

 probable by analogy that in Alydus eurinus the spermatid receives one-quarter of each of 

 the original five bivalent chromosomes. Then in the case of Fig. 101 all five elements 

 would be such derivatives ; in Fig. 1 02, five of the six elements. The sixth element of 

 Fig. 102 is then probably the original univalent chromosomes of the first maturation 

 division, which in either the first or the second maturation division could not have been 

 divided, but must have passed undivided into one of the daughter cells ; this would 

 explain why sometimes there are only five, sometimes six chromosomes in the spermatid, 

 for, as I have explained, none of the elements of Figs. 101 and 102 can be regarded as 

 chromatin nucleoli. 



Of course the preceding is only an attempt at a right interpretation ; I have not been 



able to follow the univalent chromosome with precision in regard to its behavior in the 



maturation divisions. 



20. (Jorizus lateralis Say 



Four testes of this species were studied. 



I could not determine whether there are chromatin nucleoli in the rest stage of the 



