ROBERTSON: THE CHROMOSOME COMPLEX. 299 



SYRBUI>A AD.MIRABILIS. 



and one-half are kidney-shaped. The small chromosomes (3's, 

 2's and I's) are always rods. The largest of them may show a 

 kidney shape. Sometimes in far advanced metaphases, as in 

 series 1 and 2, the second smallest (No. 2) is divided. 



A study of the chromosomes as they appear in these series 

 furnishes very strong evidence that they are discrete individ- 

 ual elements. There are three means by which chromosomes 

 may show their individuality — by size, by shape, and by func- 

 tion. Boveri ('02) proved for them an individuality of 

 function, Sutton ('02) that of size, and Baumgartner ('04) 

 that of shape or form. The series here arranged suggest 

 nothing in regard to function, but they do point to an in- 

 dividuality of size and to a certain extent of form. Of the 

 two latter characters size seems to be of most consequence. 

 The form of a chromosome seems not to be essential, for it 

 may vary to a certain extent, but the size remains the same. 

 A very clear idea of this size relation may be obtained by ob- 

 serving the second spermatocyte series, 26-29, for in any one 

 of these series all of the members except the accessory are of 

 comparatively uniform diameter, and to get the size relation 

 all we need to do is to compare their lengths. In the sperma- 

 togonial series (30, 31) exactly the same size relations may 

 again be seen. This size relation is a constant. In the first 

 spermatocytes every cell shows a series, or complex, of chro- 

 mosomes, every member of which bears to its fellows the same 

 relation in size as do those of any other cell. If any of the 

 group in the cell are large they are all proportionately large; 

 if small, they are all likewise small. The relative sizes remain 

 the same in either case. Then, too, this size relation is the 

 same from one generation of cells to the next as well as among 

 different cells of the same generation. For the proof of this 

 compare the series from the spermatogonia and second sper- 

 matocytes with those of the first spermatocytes. 



In cells from each of these generations it has been observed 

 that there are always two groups of chromosomes in the com- 

 plex that may easily be recognized, the three extremely large 

 ones (12, 11, 10) and the three extremely small (3, 2, 1). 

 They may be seen in the prophase stages as well as in the 

 metaphase. The grouping seems to be characteristic of the 

 Acrididm, for it is found in all three of the subfamilies. Sut- 

 ton ('02) described it for Brachystola, one of the CEdipodinx, 



