SPERMATOGENESIS OF THE CHICKEN 63 



cases, where the X-chromosome was not eccentric. On the meta- 

 phase spmdle, there were 17 out of 128 cells, where the bivalent 

 character of the other chromosomes was not striking enough to 

 make the difference visible. Among the anaphases, only 54 out 

 of 423 cells failed to show a lagging chromosome at one pole; in 

 these it had probably already reached its destined pole and lay 

 in the same plane with the others. A comparison of these figures 

 with those for the Barred Plymouth Rock are certainly convinc- 

 ing: the Barred Plymouth Rocks do not show enough cells with 

 an apparent X-chromosome to make it even mildly probable that 

 this is a sex chroniosome like the X-chromosome of insects. In 

 the Barred Plymouth Rock there are 11.82 per cent primary 

 spermatocyte cells with a possible X-chromosome, as contrasted 

 with 86.21 per cent in the insect. In the secondary spermato- 

 cytes, the Barred Rock has 3.06 per cent cells with an apparent 

 X', while the insect has per cent. 



We have seen then that the small proportion of cells with a possi- 

 ble X-chromosome casts some doubt on its interpretation as such. 

 We will examine next some of the individual cells where this 

 separate mass of chromatin appears, and see whether it is always 

 consistent in shape and size, that is, whether it can be regarded 

 as a definite individual chromosome of any kind whatsoever. 



The figures, both photomicrographs and drawings, plainly show 

 that the shape of the separate mass of chromatin varies. It 

 may be round, as in figures, 11 a, 12 b, 14, 16, 22 d, 27, 28 a, 

 28 c, 50, 77 and 82. It may be rod-shaped, as in figures 5, 8 b, 

 34, 49, 52, 53, 57, 65. It may be U or F-shaped, as in figures 

 9, 33, 46, 47, 48, 60, 61. It may be three-parted, as described 

 by Guyer ('09) for the Langshan cock, and shown in the follow- 

 ing figures of this paper: 10, 26 b, 43, 44, 74, 83. It may even 

 be four-parted, as in figures 45, 62, 66 and 73. Besides these, 

 there are many cells where rod-like arms project from the mass 

 of chromatin, which are rated by Guyer as X-chromosomes (figs. 

 1, 13, 29, 38, 40, 55, 56, 81). 



Even more striking than the variation in shape is the varia- 

 tion in size. This ranges all the way from a tiny speck (figs. 



