288 T. H. MORGAN 



would have to be made in order that the results be significant, 

 for only half of the eggs at most might be expected to show 

 such a chromosome reduction. I think, however, that the pres- 

 ence or absence of the lagging chromosome would make the 

 conclusion reasonably certain, I wish to express here my in- 

 debtedness to Miss Edith M. Wallace who has searched through 

 the material and picked out the critical stages. The drawings 

 are also due to her skill. 



There are shown in plate 1, figures a to/, six anaphase stages of 

 the polar spindle of the egg of P. fallax and in plate 1, figure 7n, 

 one anaphase stage of the egg of P. caryaecaulis. In none of 

 these stages is there any evidence of a lagging chromosome, and 

 since these stages range from a very early anaphase (a) to the 

 final stages when the daughter nuclei are reconstructing, there 

 is a strong presumption for the view that no such lagging chro- 

 mosome occurs. This conclusion tallies, moreover, with the es- 

 timated chromosome number. For instance, it was known that 

 in P. fallax there are 12 chromosomes in the equatorial plate of 

 the stem-mother's egg, and this same number is characteristic 

 of the somatic cells of the embryo that arises from the egg. If 

 no mistake on the latter counts have been made (the somatic 

 chromosomes are elongated, and, therefore, more difficult to 

 count) there could have beeu no loss of chromosomes in the 

 polar body. In the other species, however, where only six of 

 the eight chromosomes are apparent in most stages, it might be 

 imagined that loss of one of the attached chromosomes in the 

 polar body, while not affecting the visible count, might so alter 

 the internal relations as to furnish a new point of departure. 

 It would not be profitable here to take up at length the possi- 

 bilities involved in such a supposition. I have examined them 

 with some care, and have not found that they would furnish any 

 satisfactory solution. On the other hand, the evidence for P. 

 fallax is so clear, and the similarity in the two types in all -essen- 

 tial points is so evident, that I think we may accept this evidence 

 from P. fallax as strongly in favor of the view that all of the chro- 

 mosomes divide when the single polar body is given off from the 

 egg of the stem-mother. 



