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Fig. 12. — Similar to figure 11. Compared with the cell shown in the 

 preceding figure it is seen that the arrangement of the chromosomes is 

 different and that both are unlike that of the first spermatocyte where 

 the w-chromosome practically always lies within a ring of larger chromo- 

 somes. The upper cell in figure 11 shows how close the resemblance to 

 the first spermatocyte may be, on the contrary. Section by Wilson. 



Figs. 13-27. — Photomicrographs of smears, mostly from slides by Wil- 

 son, showing the behavior of the accessory in the second spermatocyte. It 

 will appear from these, I think, that while the accessory may lie near 

 the equatorial plate in the early and mid anaphases, when actual division 

 of the cell has occurred the position of the accessory in only one of the 

 two daughter cells may be determined. Of particular importance in this 

 connection is figure 15 where numerous cells in telophase are in focus at 

 one time. Each one of these demonstrates beyond question the unilateral 

 movement of the accessory. This area is but a small part of a much 

 larger one on the slide, where more than a hundred similar cells show, 

 without exception, the same undivided condition of the unpaired element. 

 The lagging chromosome is recognized by all to be the accessory. It is 

 seen here in all the divided cells to pass without division into but one of 

 the two daughter derivatives. In comparing these figures with those of 

 Foot and Strobell it should be borne in mind that these cells are without 

 question completely divided, that numbers of them are shown together, 

 and that the whole cell body is represented, so that there can be no ques- 

 tion of the relation between the members of the pairs of chromosome 

 groups. Their figures, on the contrary, are of single cells, mostly in early 

 or mid anaphases, in which the cell body does not appear. The con- 

 sistent behavior of the accessory chromosome in the different cell gen- 

 erations is worthy of attention also. Wherever it is found it tends to 

 isolate itself somewhat from the rest of the chromosomes and to behave 

 with some independence. The argument of Foot and Strobell is based 

 on conformity to one type on the part of the accessory as well as on that 

 of the ordinary chromosomes. The figures on plate LXXI will demonstrate, 

 I believe, that the accessory does not conform to' the processes of the 

 other chromosomes. Its isolated position in one of the two daughter 

 spermatids shown in figures 26 and 27 is just as apparent as it is in 

 each of the two daughter spermatocytes shown in figures 3-10. This 

 characteristic may also be seen in figures 20, 21 and 25. Certain cells 

 in the stages represented in figures 14, 17, 22, 23 may suggest that the 

 accessory chromosome might later divide, and it is upon such as these 

 that Foot and Strobell base much of their argument, but later and more 

 decisive stages demonstrate that it does not do so and this positive evi- 

 dence has much more value than the presumptive. It is my belief from 

 a careful study of the material and the photographs of Foot and Strobell 

 that not one instance which they figure is an indubitable case of a divided 

 accessory in the second spermatocyte. I do not believe that the in- 

 dentations in outline, or the light places in the middle of the accessory, 

 have any value as an indication of probable division, for such effects must 

 inevitably occur to delicate structures like the chromosomes in smearing. 

 I would submit that if such evidence is to be used,, the chromosomes of the 

 upper group in the anaphase of the second spermatocyte represented in 

 figure 37, plate III of Foot and Strobell, are much more certainly divided 

 than are any of the accessories for which they claim divisions in figures 

 26-46 of the same plate. 



