736 THOS. H. MONTGOMERY, JR. 
immediately into that of fig. 18, for both these cells lie within the 
same cyst.® 
The cells of figs. 16 to 19 correspond approximately to the 
stage where, in most other objects, there is an intercalated rest 
period. But in Euschistus there appears to be no rest stage, but 
at all times chromosomal boundaries may be clearly distinguished. 
I have given particular attention to this point, for it is one of 
considerable importance with regard to the question of the con- 
tinuity of the chromosomes. 
Figs. 22 to 24 lead to the leptotene stage that is shown in figs. 
25 to 28 (figs. 25 to 27 being cells from one cyst). <A good eri- 
terion of this stage is the first indication of beginning conjuga- 
tion of the still irregular idiochromosomes. There is at this period 
occasional indication of parallel grouping of some of the autosomes 
(e.g., in fig. 27), evidently the first step in the conjugation of the 
autosomes. In the leptotene condition there is certainly no 
continuous chromatin spirem developed, for free ends of certain 
autosomes may always bedistinguished. Indeed, at no time in the 
history of the spermatocytes is there a continuous chromatin 
spirem produced. This stage is evidently of short duration for it 
is seldom found. 
In nearly every stage, from the leptotene to the pachytene, 
some cells of nearly every cyst may exhibit the condition of syni- 
zesis, closely massed grouping of the autosomes. That is, syni- 
zesis of the autosomes is not limited to a particular period but 
extends over quite a series of stages, and at any one of the stages 
some cells may exhibit it while others do not. This may then bea 
* Objection might be raised that, with the seriation of my stages, cell and nuclear 
size is not always conformable. But cells in the same cyst vary considerably in 
volume. Thus fig. 9 is one of the largest cells of its cyst, the others of which were 
smaller, and figs. 16-19 illustrate cells of very different volumes but all from one 
cyst. Size of cell or nucleus is then no good criterion of stage. The matter of a 
correct seriation of stages is so important and one is so liable to make mistakes 
concerning it, that I have seriated the stages not primarily by a study of the auto- 
somes themselves, for that would be arguing in a circle, but by the seriation of _ 
other components, particularly the plasmosomes, the idiochromosomes, and the 
cytoplasmic differentiations. The reader will find, on examination of plates 1-3, 
that my seriation takes general count of the changes of all these structures. 
