TESTES OF GUINEA-CHICKEN HYBRIDS 53 



size, of stouter build, and of different shape. While each usually 

 appears as a curved body, the chicken X-element (figs. 5, 11, 12, 

 13, 14) is more curved than the other, having a U-shape with 

 both ends of the loop of the same size, while the guinea X-element 

 (figs. 6, 15, 16, 17, 18) is more comma- or pistol-shaped with 

 one end noticeably narrower than the other. While there may 

 be greater or less deviation from these types, generally in the 

 nature of unusual elongation or compression, on the whole, after 

 the observer's eye has become accustomed to the elements in ques- 

 tion, he has Httle difficulty in readily identifying the two types. 

 The X-element of the hybrid (figs. 7, 19, 20, 21, 22, 23) is clearly 

 of the guinea type. In both the chicken and the guinea the X-ele- 

 ment, instead of having its more chacteristic appeararance, may 

 occur occasionally as two closely apposed spherical chromosomes. 

 Under such circumstances the two components are of approxi- 

 mately the same size in the chicken, whereas one is always notice- 

 ably smaller than the other in the guinea. The same modification 

 may obtain in the hybrid (fig. 22), but here again the double 

 element is of the guinea type. 



While it is very difficult to secure representative appearances of 

 the X-element of these fowl by photography because of differ- 

 ences in the focal plane of its different parts, still the pictures 

 obtained^ are sufficiently clear to demonstrate the point in ques- 

 tion. Fig. 5 (5a magnified 750, and 56, 1500 diameters) is a 

 photograph of the X-element of the langshan cock. In the photo- 

 graph the typical U-shaped element appears to be more of a V, 

 but this is due to the fact that when the extremities of the chro- 

 mosome were in focus as they are in the picture, the bend of the U 

 was below the plane of focus and thus made to appear sharp-angled. 

 Fig. 6 shows in the guinea the metaphase of a dividing first sper- 

 matocyte viewed from one pole. The X-element at the top of 

 the field, is plainly seen to be narrower at one end. The focus 

 was such that its curved condition is not visible in the photograph. 

 Fig. 7 shows a dividing first spermatocyte of the hybrid, viewed 

 from one pole. What appears to be a long curved body at the 



^ The writer makes grateful acknowledgment to Dr. Charles Goosmann for the 

 microphotographs of Plate I. 



