1911] GATES—CHROMOSOME REDUCTION 323 
different methods described are to be welded into one. Perhaps 
it may also be hoped that the viewpoint here developed will help 
to stimulate some of the further investigations on this fascinating 
subject. ; 
Much of the confusion and change of opinion with regard to 
meiotic phenomena have come from the study of different stages 
of the process at different times. The earlier investigators of this 
subject devoted their attention almost entirely to the study of the 
heterotypic chromosomes or “‘tetrads,’’ and the manner of dis- 
tribution of the elements of which each was composed. It was 
chiefly in later studies that the necessity for determining the 
manner of origin of the heterotypic chromosomes was realized, 
So that the studies of the last five or six years have been directed 
mainly to an understanding of the earlier stages of meiosis, from 
the telophase of the last premeiotic mitosis to diakinesis. These 
include the leptonema, zygonema, pachynema, and strepsinema 
Stages (names, some of which involve different interpretations), 
all of which Grécorre (12, p. 2 39) prefers to include under the 
general term Synapsis. The synizesis, a special name proposed 
by McCrune (13) for the stage when the delicate chromatic 
threads occupy but a small part of the nuclear cavity, is also 
included in this period. In this paper I shall use the term synap- 
sis in its more restricted and more usual botanical sense, as equiva- 
lent to synizesis. 
The later Stages of meiosis, from diakinesis onward, are now 
Pretty clearly understood and agreed upon by most cytologists, 
Particularly those who have studied plant forms. It is the events 
of the earlier stages which are still in dispute. Some of the most 
useful contributions of the most recent papers have been with 
regard to the-earliest stages of all, from the “resting” reticulum 
of the spore mother cell to the synizesis condition. 
The use of the term “‘tetrads” as applied to the heterotypic 
chromosomes by nearly all the earlier students of meiosis, both 
in plants and animals, has led to much confusion, due to the fact 
that these bodies exhibit a great variety of forms and appearances, 
and in many cases are not tetravalent at all, but bivalent or gemini, 
and are not due to the split of a single body, but to the approxi- 
