CHROMOSOMES IN THE SPERMATOGENESIS OF THE HEMIPTERA HETEROPTERA.' 125 



{Dl. 2, di. 2) alike in volume, each transversely constricted and the two never in close 

 contact ; each of these is then a dyad, not a tetrad, therefore is univalent and the two 

 correspond to the larger pair of diplosomes of the earher stages. Then there become 

 clearly distinguishable a pair of much smaller bodies {Di. 1, di 1, Figs. 204, 205) 

 which correspond to the smallest chromosomes of the spermatogonium, and are a 

 smaller pair of diplosomes ; in the earlier prophases (Fig. 204) each of them is 

 longitudinally split, and they may or may not be in mutual contact. Therefore there 

 are in the prophases : 5 bivalent autosomes, 2 larger univalent diplosomes, and 2 

 smaller univalent diplosomes, 9 bodies in all. 



In the equator of the spindle there may l)e the same number of elements, or 

 there may be only 8 (Figs. 205, 206). This results because the smallest diplosomes 

 may be joined end to end (as in Figs. 206, 207, /-'/. 1, di. 1) or be placed side by side 

 (Fig. 208, Di. 1, di. 1); in either case, however, a whole one of these passes without 

 division into one of the daughter cells, which amounts to a reduction division of the 

 pair, and to each appear to be attached mantle fil:)i-es from only one spindle pole. 

 The 2 larger diplosomes [Di. "2, di. 2, Figs. 206-208), which are recognizable by being 

 dyads of equal volume and next in order of size, remain separated from each other, 

 and each by dividing along the plane of its previous constriction divides equationally. 

 The remaining, largest, chromosomes are all tetrads (the unlettered ones of Figs. 206- 

 208), and these divide reductionally, because each divides transversely to its long 

 axis. Each second spermatocyte receives accordingly 5 whole autosomes, a whole 

 diplosome of the smaller pair, and a half of each larger diplosome, a total of 8 elements. 



Second Maturation Division. — Here there are on pole views (Fig. 209) always 

 only 7 chromosomes visible, 5 larger and two much smaller. The five largest are 

 clearl_y the autosomes. The two smaller must then correspond to the 3 diplosomes 

 that each second spermatocyte receives, i. c, one of them must be bivalent. Lateral 

 views (Fig. 210, which shows all the elements) demonstrate that each of the smaller 

 elements is composed of two parts of equal volumes. Therefore there could not have 

 taken place a conjugation of a large with a small diplosome, Ijut twtj diplosomes of 

 equal volumes must have conjugated. Now since we found that the second sjjerma- 

 tocyte receives only one diplosome of the smaller pair, but a half of each of the 

 larger, and since the latter wei'e of ecjual volume, it is these larger ones that must 

 conjugate, come to lie the one immediately above the other, in the second spindle 

 Accordingl}', of the 6 elements shown in Figs. 209 and 210, the 5 largest are univalent 

 autosomes, the smallest {di. 1) is one univalent diplosome of the smaller pair, while 

 the next smallest, the central one, is bivalent {Di. 2, di. 2). This explanation suf- 

 fices to make clear the change in number from 8 to 7 in conjunction with the per- 

 sisting size relations. 



