2ffB KANSAS UNIVERSITY SCIENCE BULLETIN. 



was a divided accessory chromosome found in any second 

 spermatocyte. For a short time the accessory chromosome 

 lies against the mass of chromosomes, but when the spermatids 

 are separated and the nuclei re-form it moves away again and 

 lies at one side. Such conditions are shown in plate LXXI, fig- 

 ures 20-21, 25-27. No clearer or more precise demonstration of 

 a cytological fact could be asked than is here afforded by the 

 unilateral movement of the accessory chromosome. 



The question naturally arises, why, if this be true, should 

 two observers decide that the accessory chromosome does here 

 divide? It is of course, impossible to explain just why this has 

 occurred, but it would seem to me that Foot and Strobell were 

 impressed with the necessity of showing every chromosome in 

 both daughter cells and that they chose stages which exhibited 

 such arrangements. Since it is impossible to find these con- 

 ditions after a mid-anaphase, owing to the massing together of 

 the chromosomes, all their pictures were made in the early 

 anaphase while the accessory chromosome lies in or near the 

 equatorial plate. Not a single photograph of an unmistakably 

 completely divided second spermatocyte is shown among all 

 their figures. Since it is only at this time that the accessory 

 chromosome may definitely be demonstrated to occur in only 

 one daughter cell their failure to figure it may be understood. 



Since Foot and Strobell base their case upon the evidence 

 afforded by their photographs, it is proper that these should 

 be considered. They show in plate III twenty-three figures of 

 second spermatocyte anaphases and telophases. In all but 

 figure 45 the accessory chromosome lies undivided in the equa- 

 torial plate, and in this two independent nuclei with no clearly 

 marked accessory chromosomes are advanced as evidence that 

 the accessory chromosome has divided. Figure 46 shows aho 

 two nuclei with no indication that they are daughter deriva- 

 tives. Figures 29, 30, 31 and 44 are introduced to show the 

 actual division of the accessoi-y chromosome. Figure 29 shows 

 the accessory chromosome of a mid-anaphase with a slight 

 constriction at the center, figure 30 a similar cell with two 

 distorted and ill-defined chromosome masses, figure 31 two 

 other similar daughter groups with an apparently divided lag- 

 ging chromosome, while figure 44 exhibits a mid-anaphase with 

 the daughter ( ?) groups widely separated and turned by spread- 



