CHROMOSOMES OF INDIAN RUNNER DUCK. 335 



was moistened and laid along the median curvature of the 

 chromosome outline. By means of a razor blade its ends were 

 cut at points corresponding to the boundaries of the ends of the 

 chromosome as the thread lay upon the drawing. The segment 

 was then removed and drawn out straight and measure taken in 

 millimeters. In this way with a considerable degree of accuracy 

 the length of the chromosomes was obtained. 



CHROMOSOMES OF THE SOMATIC CELLS. 



In the duck it will be more convenient to consider first the 

 complex of the male (Figs. I to 7 and 43 to 48) since it is in this 

 sex that the number of chromosomes is even. 



There are probably seventy six. Some deviation from this 

 number was found in the early part of the work. This was due, 

 in greater part, to a failure to recognize the small globe-shaped 

 chromosomes. For a time they were thought to be basophylic 

 knots on the filaments that sometimes occur between the smaller 

 chromosomes. As the work progressed, however, it became 

 more apparent that these were true chromosomes. In addition 

 to this deviation about half a dozen cells were found in the amnion 

 in meta phase that appeared to have but half the usual number of 

 chromosomes (thirty-eight). At this time no explanation can 

 be offered for this condition. With the exception of the above 

 few cases all cells examined, in which the chromosomes were well 

 separated, seemed to have seventy-six. I am inclined to think 

 that this is the basic number. 



These seventy-six chromosomes fall readily into three general 

 groups: six pairs of large chromosomes, including three J-shaped 

 and three rod-shaped; nine pairs of short rod-shaped chromo- 

 somes; and twenty-three pairs of globe-shape. This may be 

 seen in Figs. 43-48, Plate 8, which is an artificial pairing of these 

 chromosomes arranged according to size. The morphology and 

 the length were taken as a basis for this pairing. Where there is 

 a slight difference in the lengths of the members of a pair, the 

 shorter member is usually broader at one end than its mate. 

 This makes the chromatic material of each member approximately 

 the same. 



Of the six pairs of large chromosomes (Nos. 38-33) the largest 



