138 CHROMOSOMES IN THE SPERMATOGENESIS OF THE HEMIPTERA HETEROPTERA. 



First Maturation Division. — In the spindle there are lOcliromosonies (Plate XIII, 

 Figs. 295, 296). The smallest of them (j1/o, Fig. 296) is never in the equatorial plane 

 but always nearer one of the spindle poles ; it does not divide but passes bodily into 

 one of the spermatocytes of the second order. This minute element would appear to 

 be a monosome, comparable to the smaller monosome of Calocoris. There is no sign 

 of it in the chromosomal plate of the following mitosis. Of the 18 elements that lie 

 in the equator (Fig. 295) all divide in this mitosis. Two of them (Di. 1 and I)i. 2, 

 di. 2) are much smaller than the others ; the smaller of the two (Di. 1) is a univalent 

 diplosome as its later behavior shows, while the larger is a V^ivalent element and it may 

 be a pair of diplosomes (though its small size is tlie only reason to consider it a diplo- 

 some). Of the 16 large elements one of the largest, if not the veiy largest, must be 

 another univalent diplosome, which with the small element Di. 1 are unequal com- 

 ponents of a diplosome pair. 



Second Maturation Division. — There are always exactly 17 elements to be seen 

 on pole views of the spindle (Fig. 297), 2 less than in the preceding spindle ; this 

 number was found in numerous cases. All are larger than the small monosome of the 

 antecedent mitosis, and this monosome is not to l)e found in the chromosomal plate ; 

 one would expect to find it in the equator of half of the second spermatocytes, as is 

 the case with the cori'espondent element in Calocoris; but it is always absent, and 

 therefore probably lies out in the cytoplasm where it is indistinguishable from siunll 

 yolk spherules. Further, in the equator there is only one separate small element 

 (Fig. 297, Di. l^), and not 2 separate elements (as in the preceding spindle, Fig. 295, 

 Di. 1, Di. 2). Careful study shows that one of the chromosomes is bivalent, composed 

 of a small one (/>/. 1, Fig. 298) placed at the end of a much larger one [di. 1), tlie 

 larger one lying invariably a little above or below the equator which enables one to 

 recognize it upon pole view (di. 1, Fig. 297). This bivalent chromosome is composed 

 of the division products of the largest and smallest diplosomes of the first spermato- 

 cytes, which had divided separately but are now in conjugation. The single separate 

 small element [Di. J, Figs. 297, 298) again divides by itself; it is a little larger than 

 the smaller element of the l)ivalent pair and therefore represents a half of the bivalent 

 element Di. 2, di. 2 of the former mitosis. The 15 autosomes also divide, and the 

 bivalent diplosome divides reductionally, its smaller component going into one sper- 

 matid and its larger one into the f)ther ; for this becomes evident from their position 

 within the spindle (Fig. 298, Di. 1, di. 1), while in the anaphases the lai'ger compo- 

 nent (Fig. 299, (//. i) comes to lie wholly' in one of the daughter chromosonjal plates. 



There are accordingly in the maturation mitoses : one very small monosome that 

 does not divide in the first sperm atoc^'te, and is not present in the chromosomal plate 



