NOWLIN : CHROMOSOME COMPLEX OF MELANOPLUS. 269 



tudinal split. One program of movement is closely adhered 

 to in every case. The longitudinal split runs from one end of 

 the bivalent chromosome to the other, and separation along this 

 split begins at the place of union of the two univalent elements, 

 as shown in figure 2, chromosome 4. It is in this condition that 

 the chromosomes sometimes enter the spindle, their long axis, 

 or the longitudinal split, parallel with the equator (pi. XVII, 

 cell G, row 7). More often, however, division has continued 

 to the point where the arms of the cross are equal (pi. 2, 

 cell A, row 8), or even farther, as in cell A, row 9. The chro- 

 mosomes of this complex divide very irregularly as to time, 

 some having almost completed the separation while others are 

 but beginning. This variation is seen in plate XVII, cell G. 

 Chromosome 11 seems to be precocious. The ring chromo- 

 some, No. 10, divides slowly, as might be expected, and, like 

 the others, shows the first division to be longitudinal. Its be- 

 havior is entirely different from such rings as are found in 

 the beetles, where the two bivalent elements separate in the 

 first spermatocyte (Stevens, '06; Nowlin, '06). 



The ring has some significance in this material — not that 

 its occurrence is unique, but because of the constancy of this 

 form of chromosome for different species. A single ring seems 

 to be constant for Melanoplus bivittatus, while in one of the 

 Tryxalines, Syrbula admirablis , now under investigation by 

 Mr. Robertson, there are five rings. 



There is little difficulty in seeing that a chromosome which 

 enters the spindle with its longitudinal split at right angles to 

 the long axis of the spindle divides longitudinally in the first 

 spermatocyte. The spindle fibres are attached at right angles 

 to the split (pi. XVII, cell G, row 7) and consequently pull the 

 halves apart along this split. But a chromosome like No. 12, 

 which enters the spindle with its longitudinal split parallel 

 with the long axis, may cause confusion. On account of its 

 great size this chromosome can be easily followed through the 

 different generations. In a polar spermatogonial view (fig. 1, 

 chr. 12) it is seen to be long and rod-shaped, about eight times 

 the volume of the smallest. No. 1. In the early prophase we 

 recognize it again by the great size (fig. 2). In the late pro- 

 phase we see it in the form of a cross (fig. 8), and in meta- 

 phase (fig. 10a, chr. 12) again as a rod. There is but one ex- 

 planation: the chromosome during the prophase begins to 



