ROBERTSON: THE CHROMOSOME COMPLEX. 297 



SYRBULA ADJIIRABILIS. 



been explained by others and once already in this paper, con- 

 sists of two homologous spermatogonia! chromosomes joined 

 together by their ends, proximal end with proximal and distal 

 with distal. The proximal ends are always united, but the dis- 

 tal ends may or may not be. Sometimes they are so firmly 

 joined that the distal end or region of the ring cannot be told 

 from the proximal except by the fact that the proximal por- 

 tion always points towards or lies nearest to the center of the 

 cell-plate. In these tables (plates XXI and XXII) the rings 

 are always placed as nearly as possible in a position with the 

 proximal portion uppermost. In the case of the kidney-shaped 

 or bent-rod forms in columns 8, 6, 4 and 3, and any similar 

 chromosomes that may occur in other columns, the proximal 

 end or part (the convex side) of the chromosome is turned 

 towards the left. To be logical this portion in these chromo- 

 somes should have been turned upwards, as in the ring forms, 

 but less room was required the other way. In the case of the 

 accessory the proximal end is again as far as possible placed 

 uppermost. In series 26-31, from the spermatocytes and the 

 spermatogonia, the proximal end, that to which the fibers are 

 attached, is always placed uppermost. 



In the formation of the rings quite often the distal ends are 

 imperfectly or not at all united, but the polar or proximal ends 

 are always united. It does not seem to be necessary that the 

 distal ends shall always unite, but there is a tendency for them 

 to do so, and this tendency is greater in certain individual chro- 

 mosomes than in others. In general, the larger chromosomes 

 seem to be more inclined to form rings than the smaller. Nos. 

 12 and 11, according to these cells, are always rings or ring- 

 like forms. Some possible exceptions occur, principally in the 

 second column (chromosome 11 in series 2, 8, 19, 22 and 23) 

 where the distal ends are either imperfectly or not at all 

 united. But nevertheless the distal ends of the pair bend 

 around toward each other, showing that they have a tendency 

 to unite and form a ring. In series 5 and 6 of column 10 two 

 notable exceptions occur: that in series 5 is somewhat in- 

 clined to form a ring, but that in 6 has no inclination whatever 

 to do so. In series 18 the distal ends of No. 10 seem to have 

 glided past each other. In such as that in 15, 16, 20, 21 and 

 23 the distal ends have not moved past each other, but they 

 evidently did not meet exactly on end, as is shown by the 



