56 
Franz Schräder 
\Tridissima (Mohr, ’14a), which when provided with an homologous 
mate, as it is in the female, behaves exactly as do the autosomes. But 
this wiW not explain all cases of exceptional chromosome behavior, and 
certainly in the m-chromosomoe of Alydus pilosulus condensation occurs 
earlier than in the autosomes, despite the fact that two m-chromosomes 
are present (Wilsox, ’05). 
The distinctive beha%dor of heterochromosomes may differ in various 
animals. Thus in some species, this behavior will already characterize 
the prophases of embryonic cells, in others it will first appear in the sper- 
matogonia, and finally, it may not become apparent until the spermato- 
cytes. The main points of this behavior in an animal like Locusta are as 
follows: Düring the resting stages of the spermatogonia, the monoseme 
never becomes as diffuse as the autosomes. At certain stages of the pro- 
phase it lies in a special little vesicle. Its evolution and condensation 
parallel that of the autosomes but occur somewhat in advance of them. 
Moreover it is always located at the periphery of the nucleus. These 
characteristics, vdth the exception of the vesicle formation, are found 
also in the spermatocytes, where, however, the monoseme tends to remain 
more Condensed or eise to go through the prophase stages in a more limited 
space than in the spermatogonia. There also, when its contours have 
become rounded and smooth, the equational split is a plain and distinct 
feature. These points as described in Locusta (Mohr, ’14a and b) are 
supplemented by others which have been observed elsewhere. Thus 
there is a tendency for multiple X chromosomes to stay together and 
move to the same pole at reduction, as illustrated by Syromastes (Wilson, 
’09). And finally, when the chromosomes become diffuse in the spermatid, 
it is the heterochromosome that lags behind the autosomes in this respect 
and stains intensely even after the latter have become a lightly staining, 
flocculent material in the nucleus. 
How then do the five chromosomes of Pseudococcus, which evolve 
in advance of the remaining chromosomes, com-pare with such a hetero- 
chromosome? A distinctive behavior on their part can at first be definitely 
observed in spermatogonial prophases, where they are Condensed before 
the remaining five chromosomes. This feature which distinguishes two 
groups of chromosomes, is still more more marked in the spermatocytes. 
There the chromosomes first evolved are always located at the periphery 
of the nucleus and betray an undoubted tendency to clump together. 
At reduction they move to one pole as a unit, and finally, in the sperma- 
tids they retain their staining capacity and general shape while the sister 
group becomes diffuse. It is only in their failure to form chromosome 
