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64 ALICE M. BORING AND RAYMOND PEARL 



2 b, 2 c, 14, 49, 51) up to a piece almost half the volume of the 

 whole chromatin mass (figs. 7 b, 8 b, 25 b, 25 c, 43, 75). 



Beside the above-mentioned inconsistencies in shape and size, 

 in some cells there is more than one separate piece of chromatin. 

 Figures 10, 27, 48, 49, 53, 83 show two separate chromosomes, and 

 figure 28 c shows three, while figure 75 may show four. These 

 are cases where the two or three X-chromosomes are all dis- 

 tinctly separated from the chromatin plate. If one counts the 

 projecting arms and pieces lying close to the large mass, yet ap- 

 parently separate chromosomes, there are many more cases with 

 more than one X-chromosome. Figure 1 has four arms; figure 

 28 a has one round X-chromosome and one arm ; figure 46 has 

 one F-shaped chromosome and one arm; figure 49 has one round 

 odd chromosome, one rod-shaped and one arm; figure 52 has one 

 separate rod and one rod-like arm; figure 61 has one F-shaped 

 element and two arms. If it is legitimate to call an arm an X- 

 chromosome when there is no separate chromosome to call X, 

 then it ought to be equally legitimate to count an arm as an X- 

 chromosome, when a separate chromosome is present, and to 

 conclude that there is more than one X-chromosome in such 

 cases. 



A study of the anaphases shows that in this Barred Plymouth 

 Rock material, a lagging condition, as indicated by a projecting 

 arm cannot safely be regarded as indicating a real difference in 

 behavior from other chromosomes, for there are in actual fact 

 as many cases with corresponding lagging arms at both poles of 

 the anaphase spindle as with one at only one end. Figures 18 b, 

 19, 21, 67, 68, 69 are spindles where this is the case. This evi- 

 dently means merelj^ that these Barred Plymouth Rock chro- 

 mosomes do not always separate as evenly and as synchronously 

 as those in insect material. 



We have seen that the so-called X-chromosome of the Barred 

 Plymouth Rock male germ cells varies in shape, size and num- 

 ber. If it is such a variable element, it is evident that many of 

 the figures used in this paper are capable of varying interpreta- 

 tions. Let us run over the figures to see what possible interpre- 

 tations we find for some of them. Figure 1 is a primar}' spermato- 



