Studies on Chromosomes. 383 



size. The first spermatocyte-division shows 8 chromosomes, 

 which differ in grouping from that of the other forms in that all 

 usually lie in a ring without a chromosome at its center (Fig. 4 

 a, />). For this reason no clue to the identification of the idiochro- 

 mosomes is given by their position. Two of the chromosomes are, 

 however, distinctly smaller than the others; and the relations in 

 the spermatogonia leave little doubt that it is these two that corre- 

 spond to the idiochromosomes. They may lie side by side (Fig. 

 4*3) or more or less widely separated (4^). All these chromosomes 

 are, in side view, seen to have a symmetrical dumb-bell shape, and 

 all are equally halved in the first division. None of the prepara- 

 tions show the stage immediately following; but there can be no 

 doubt that a conjugation of the two small chromosomes takes 

 place at this time, since the second division (of which I have a large 

 number) invariably shows in polar view but 7 chromosomes, which 

 have now assumed the usual arrangement, with one in the center 

 of a ring formed by the 6 others (Fig. 4<r). Nezara differs again, 

 however, from all the other forms in the fact that the small chro- 

 mosome (/'. e., the idiochromosome-dyad) lies in the outer ring, 

 in many if not in all cases, while one of the larger chromosomes 

 lies at the center of the ring. Lateral views of the spindle show 

 all of the chromosomes as quite symmetrical dyads; and in the 

 ensuing division all divide equally (Fig. 4^). In such views the 

 idiochromosome-dyad, which is readily recognizable by its size, 

 may be clearly seen to divide equally; and in this respect Nezara 

 differs from all the others. The anaphase sister-groups of the 

 same spindle, each containing 7 chromosomes (Fig. 4^, /) are, 

 accordingly, exact duplicates, the idiochromosome retaining its 

 position in the outer ring. 



The symmetrical division of the idiochromosome-dyad in Nez- 

 ara is a fact of importance for the comparison of the idiochromo- 

 somes with the microchromosomes of such forms as Anasa or 

 Alydus. Were it not for their failure to unite to form a bivalent 

 body until the end of the first mitosis we should find no ground in 

 this case for designating these chromosomes by a special name. 



2 The Spcrmatogonial Chromosomes. 



We have now to examine the relation of the chromosomes of 

 the first maturation to those of the spermatogonia. The material 



