The Chromosomes of Gryllotalpa Borealis Burm. 
145 
Gryllotalpa, but if this double X-eleraent arose in tbese forms by the 
breaking up of the large idiochromosome as suggested (Payne ’09), it 
is possible that this chromosome combination in Gryllotalpa arose in 
the Same way and that an intimate association once existed between 
the large idiochromosome and the odd chromosome, but has been lost. 
It must be admitted, I think, that this interpretation fits in more nicely 
with previous work along this line and offers no obstacle to the various 
theories of sex production based upon the sex chromosomes. 
If we consider Gryllotalpa as an isolated case, the evidence is cer- 
tainly in favor of the tlürd interpretation, that is, that there is present 
in this form an unequal pair of idiochromosomes and an odd chromosome. 
' The behavior of the odd chromosome is typical of those previously de- 
scribed. It passes undivided to one pole in one division and divides 
i equally in the other. Also the behavior of the unequal pair of idiochromo- 
somes is typical of those desctibed by Stevens in Tenebrio and certain 
I Diptera (’05 and ’08). The two components separate in the first division 
I and each divides in the second. As previously stated, an intimate asso- 
I ciation exists between the members of the double X-element in Cono- 
rhinris, Fitchia and Thyanta. They not only move to the same pole in 
the second division, but lie dose together and move as a unit. In Gryllo- 
I talpa there is no connection between the large idiochromosome and the 
odd chromosome other than that they both move to the same pole in 
the first division. They may or may not lie dose together and they do 
not move as a unit, the odd chromosome always moving far in advance 
of all the other chromosomes. The fact that here we find two chromo- 
somes which can be identified as passing to the same pole need not ne- 
1 cessarily mean that a more intimate association once existed between 
1 them. While it has been assumed that the arrangement of the chromo- 
j somes on the spindle is a haphazard one, especially by those who have 
I looked upon the chromosomes as a basis for an interpretation of Mendelian 
I heredity, it by no means is an established fact that such is the case. 
I 
I 
! Origin of the Chromosome Combination in Gryllotalpa. 
j There are two possible explanations of the origin of this chromo- 
I some group. First, as previously suggested the original condition may 
! have been an unequal pair of idiochromosomes and the odd chromo- 
some may have arisen by the breaking up of the large idiochromosome 
into two parts. These two parts, instead of acting as a unit as in the 
I Reduviidae and Thyanta have lost all traces of connection except that 
' Archiv f. Zellforschung. IX. 10 
i 
