Katharine Foot and E. C. Strobell 291 
chromosomes of the dense dyads of the earlier stages and when at these 
stages the identity of the eccentric is obscured we certainly are justified 
in not confounding it with these dense dyads. 
The characteristic form of the eccentric chromosome with its longi- 
tudinal furrow assures its identification through the prophases, meta- 
phase, and in some cases the anaphase of the first spindle. Beyond this 
stage its eccentric position is the strongest evidence of its identity, but 
as this relatively isolated position is typical of this chromosome in the 
earlier stages we may accept it as evidence of its identity in later stages 
also. Even in those first metaphase stages in which the chromosomes are 
almost in a straight line the eccentric has typically a more or less 
detached position and when not distinctly isolated is generally found 
at one end of the line of chromosomes. This is shown in Photos. 22, 23, 
25, 26, and 27. In the last photograph the eccentric is at the right end 
of the line of chromosomes and a dense dyad is at the left end of the line, 
but this latter chromosome is dividing transversely and cannot be confused 
with the eccentric which shows its typical longitudinal furrow. 
Photos. 28 to 32 are of preparations showing the early anaphase of 
the first division. In four of these five preparations all the eleven chro- 
mosomes can be counted and at least three of the preparations demon- 
strate a foreshadowing of a second division for the eccentric chromo- 
some. We believe that the form of this chromosome during the pro- 
phases and metaphase demonstrates that it divides longitudinally at the 
first division while the other chromosomes divide transversely. This 
difference in the plane of division of the eccentric has been noted by 
Montgomery, 06, and figured in his sketch 138. In Photos. 28, 29, and 
30 we interpret as the eccentric chromosome that chromosome which in 
each case is furthest to the left of the group. This interpretation we 
base, first, on its slightly isolated position, and second, on the fact 
that the plane of its division is more suggestive of a longitudinal division 
than is that of any of the other chromosomes. ‘This is especially true 
in the case of Photo. 29, and in both Photos. 28 and 30 the two halves 
of this chromosome show a distinct indication of a longitudinal furrow. 
It is possible that this may not be demonstrated in all the reproductions, 
but in the original photographs it is beyond question. In Photo. 30 this 
same secondary furrow is demonstrated in all the ten large chromosomes, 
therefore, if our identification of the eccentric is questioned we still 
cannot avoid the fact that the eccentric, wherever it is, has—in common 
with the rest of the chromosomes—a secondary furrow, and this holds 
true also for Photo. 32, in which the identity of the eccentric is ob- 
