A Comparative Study of the Chromosomes etc. 
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paifed rr-chromosome by the subtraction oi y+y from xy + y. The ques- 
tion immediately arises, what has become of y+y in forms which have 
au impaired a>chromosome {E. curvata for instance)? Does y+y form 
a separate pair of chromosomes, either different from or similar to the 
autosomes in the growth period (for the ?/-chroniosome stains deeply in 
forms having paired idiochromosomes), or is the substance of y+y taken 
up by the autosomes? I shall return to a consideration of this question 
in a discussion of the probable origin of the unpaired a>chromosome of 
E. curvata. 
2. The sex chromosomes are usually characterized by their form 
and stainability in the growth of the spermatocyte; they remain Condensed 
and seldom lose their affinity for basic stains to the same degree as do 
the autosomes. Gases have been described in which the allosomes are 
vacuolated or are intiniately associated with plasmasomes during the 
growth period of the sperniatocytes (Wassilieff ’07, Dederer ’07, 
Büchner ’09, Payne ’09). Both Büchner and Wassilieff attribute 
to the x-chromosome the production of cytoplasmic granulös or mitochon- 
dria. The x-chromosome is often surrounded by a clear area of cytoplasm 
(as in E. curvata), which may indicate sonie special metabolic activity 
of this body affecting the autochromatin. Brunelli (’IO) has suggested 
that the a;-chromosonie may be associated with the transformation of oxy- 
chromatin into basichromatin in the formation of the tetrads at the end 
of the growth period. All these cases would seem to indicate that there 
is a special “x-chromatin”, physiologically different from the “auto- 
chromatin”. Goldschmidt (’IO) and Büchner (’09, ’IO) have considered 
the x-chromosome merely as a special configuration of tropho-chromatin, 
comparable to Giardina’s ring and to basic nucleoli of oöcytes, but not 
a true chroniosome. The last conclusion is hardly justifiable, for in oögonia, 
spermatogonia and soma cells of animals possessing definite sex-chromo- 
somes it is known that the behavior of these bodies in mitosis is similar 
to that of the autosomes. That they may be different physiologically but 
still be chromosomes is not unlikely. However, we cannot have a clear 
idea of their function until a careful comparative study of their behavior 
in the oöcytes and spermatocytes of the same species has been made. 
3. The behavior of the components in the case of the paired idio- 
chromosomes seems to differ in the various Orders of insects. In the 
spermatogenesis of Orthoptera (Randolph ’08, Stevens ’IO) they unite 
just before the fh’st maturation spindle is formed. This has also been 
shown to be the case in many Coleoptera and Diptera (Stevens ’06, ’08, 
’09a). In the Hemiptora (heteroptera) the idiochromosomes fail to unite 
