Katharine Foot and E. C. Strobell 293 
2, 3, 4, 8, 10, 14 to 18, Plate III, in which the characteristic position 
of the eccentric chromosome is clearly shown. It seems to us that in 
these preparations the identification of the eccentric as the chromosome 
outside the circle is almost as certain as the identification of the micro- 
chromosome within the circle. 
We believe that the frequent eccentric position of this chromosome 
offers at least a partial explanation of its retarded division. If the divi- 
sion of the chromosomes is dependent in any degree upon forces centered 
at the poles, one chromosome isolated from the group would certainly 
be less under the influence of this force and its response would, therefore, 
be slower, resulting in a retarded division. It is easy to conceive further 
that such a condition started in the first spindle could be exaggerated in 
the second, and in fact might often result in the entire omission of the 
division of the isolated chromosome. But we believe such a condition 
to be abnormal in view of the fact that we can demonstrate the division 
of the lagging chromosome not only in the first spindle, but also in the 
second. If we are right in our surmise that the more or less isolated 
position of this chromosome may be in a measure responsible for its fre- 
quent delay in division, we should expect to find in all forms in which 
dimorphism of the spermatozoa is claimed, some evidence that one 
member of the chromosome group may have a more or less detached 
position, such as we find in Anasa. An examination of the literature 
shows a very suggestive number of cases in which one of the chromosomes 
of the first metaphase has an eccentric position very similar to that of 
the eccentric chromosome of Anasa tristis.” We shall not attempt to 
enumerate these cases, however, for the reason that in many of them 
this eccentrically-placed chromosome is not identified with the chromo- 
some, which later, by its unequal division gives rise to the dimorphism 
of the spermatozoa. The force of this adverse evidence is, however, 
weakened when we recall that both Paulmier and Montgomery at first 
interpreted the lagging chromosome of the second spindle as one of the 
microchromosomes—its identity with the eccentric chromosome being 
first recognized by Wilson several years later. 
Plate III, Photo. 1, shows a late anaphase or telophase of the first 
spindle in which a daughter half of the lagging chromosome lies mid- 
way between the poles. ‘This chromosome belongs to the left pole, for 
>The possible meaning of such an arrangement of the chromosomes is of 
course another question, and speculation as to its significance may well be 
deferred until far more exact data have been collected, not only for this form, 
but for many more forms. 
