AND OF HYBRID PIGEONS. 
17 
in Fentatoma could be seen. Chromosomes could be distin¬ 
guished in fact, only after the nucleus had passed through a 
spirem stage, when, as has been noted already, the chromatin 
appears laid down in half the original number of chromosomes; 
that is, the new chromosomes are of the bivalent type. 
As to the meaning of synapsis, we seem to be in almost 
total ignorance. P'ew suggestions seem to have been proposed 
to explain it beyond that of Moore^ who mentions the possi¬ 
bility that it may mark an abortive attempt to bring about the 
formation of a tailed spermatozoon, due to a sort of historical 
reminiscence which m*arks this as a once final stage of develop¬ 
ment in the remote ancestral sex cells. It seems to the writer 
more probable that the fusion is a conjugation of maternal and 
paternal chromosomes, though why such is necessary, is not 
apparent. Some rather significant facts appear which may fur¬ 
nish a possible clew to the nature of some of the changes which 
occur during the period of nuclear collapse. A very careful 
determination of the size and shape of the nucleus and sphere 
substance respectively was made in a number of cases just 
before and during the contraction of the contents to one side. 
Immediately before the change, the large nucleus is nearly 
spherical, or if oval, its long axis may lie in any direction with 
reference to the sphere. After the contraction has occurred, 
the nucleus is always slightly flattened toward the sphere; that 
is, the long axis of the oval lies parallel to the sphere. More¬ 
over, at times the nuclear membrane is a trifle wavy or uneven. 
The average diameter of the nucleus before is slightly greater 
than during the period of apparent collapse. A large number 
of measurements of the sphere reveals the, fact that it is, on an 
average, almost a third larger after the chromatin has massed 
nearer it than before. This, together with the fact that the 
drifting of the nuclear contents is always toward the sphere, 
and that the nuclear membrane is indistinct in that region, leads 
to the conclusion that there has been a discharge of part of the 
nuclear material into the sphere. Then, too, occasional frag¬ 
ments of chromatin are seen scattered about in the sphere, 
indicating that they have been carried out, perhaps during a 
discharge of the material from inside the nucleus. Again, the 
1. Loc. cit., p. 16. 
