SPERMATOGENESIS OF THE CHICKEN 65 



cyte equatorial plate. It has four projecting arms. Perhaps 

 these are four X-chromosomes. But two arms are longer than 

 the others. Perhaps only the two longer arms are X-chromo- 

 somes. The two long arms are rod-shaped, while the two short 

 ones are rounded. If there is only one X-chromosome and that 

 is round, it must be one of the short arms; if it is rod-shaped, it 

 must be one of the longer. If there are two X-chromosomes, one 

 might be rod-shaped and one round, or both might be round, or 

 both might be rod-shaped. Or it might much more probably 

 be that there is no X-chromosome at all, and all four arms are 

 only ordinary bivalent chromosomes, which happen to project a 

 little from the plate of chromosomes. 



Figure 4 is a primary spermatocyte equatorial plate and may 

 have a round X to the left and a rod-shaped one to the right, or 

 either one of them may be X, while the other is a bivalent chrom- 

 osome. Or again, there is nothing about either which stamps it 

 even probably as an X-element, so there may be no X at all. 



Figure 12 b is a first spermatocyte equatorial plate and may 

 have either one or two X-chromosomes, according to whether 

 one counts the round body which touches the mass of chromo- 

 somes as one or not. It does not happen to be quite as far away 

 as the entirely separate one, but there is no other indication of its 

 being different in character. 



Figure 13 is a side view of a primary spermatocyte metaphase 

 spindle, the arm to the left, pointing toward the upper pole may 

 represent an unpaired chromosome, but on the other hand, there 

 is no surety that this is univalent, while the rest of the mass is 

 composed of bivalent chromosomes. 



Figure 33 is a first spermatocyte metaphase spindle. The 

 body to the right may be a F-shaped X-chromosome, or it may 

 be a three-parted X-chromosome, or it may be an ordinary dumb- 

 bell-shaped bivalent chromosome in the process of dividing. 



Figure 18 b is a first spermatocyte anaphase. Any one of the 

 three arms to the left might be a lagging X-chromosome, but 

 the general scattered condition of the chromatin would make it 

 just as reasonable to interpret all three as ordinary chromosomes. 

 The middle one at least has a mate at the right pole. When 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 16, NO. 1 



