282 
Sidney 1. Kornhauser 
uiitil the second niaturation division, at which time they come together 
end to eud and subsequently separate reductionally (Wilson ’Oöa, ’Oöb, 
’06; Moxtgomery ’OO, ’ll). The allosomes certamly exhibit less affinity 
for each other than do the autosomes. In E. hinotata it was shown that 
the xy pair was formed (alter the pairing of the autosomes) in the zj'go- 
nema by an end to end fusion of two threads followed later by their ap- 
proxiniation side by side. In the Orthoptera and Coleoptera this union 
occurs still later, and in the Hemiptera (heteroptera) it is delayed until 
the second spermatocyte division. Can we in any way account for the 
Variation in the degree of attraction or repulsion which these chromo- 
somes exhibit toward each other? If we assume that the idiochromosome 
pair is represented by the formula xy + y, and that y and y tend to 
attract each other (perhaps representing the basis of allelomorphic cha- 
racters), while the “a;-chromotin” is indifferent to “y-chromatin” or “auto- 
chroniatin”, then the attraction between the large idiochromosome and 
the small idiochromosome would depend upon the amount of “y-chro- 
matin” still remaining in the large idiochromosome (assuming that y+y 
tend to separate froni xy+y). 
4. The deportment of the y-chromosome and “y-chromatin” is of 
utmost importance in a consideration of the probable origin of the un- 
paired a-chromosome frorn a pair of idiochromosomes. Formulating 
the paired heterochromosomes as xy+y, it is logical to suppose that in 
its unniodified form xy (the larger idiochromosome) should contain more 
chromatin than y (the smaller idiochromosome). This seems to be true 
of the majority of cases, for only a very few examples of equal hetero- 
chromosomes have beeil described: Oncopeltus (Montgomery ’06, Wil- 
son ’lla), Änisolabis (Randolph ’08), PMlosamia (Dederer ’07), and 
other Lepidoptera (Cook ’IO). In E. linotata it was shown that, although 
it was impossible in metaphase to distinguish in size between the two 
components of the allosome pah, yet the behavior of its two components 
in the growth period showed that one contained more stainable sub- 
stance than the other. This might indicate that it may not always be 
the amount of chromatin which determines the size of a chromosonie, 
but that size may also depend upon the linin which forms the ground- 
work for the chroniatin. 
In Acholla multispinosa (Payne ’09) the ^-chromosome is larger than 
the ic-complex, which is made up of five chromosomes. It is possible 
that here we have a case in which tliere is a breaking up of the x- chronio- 
some and a loss of some of its “i/-chromatin”, which tends to link itself 
to the original ^-chromosonie. 
