250 GERM-CELL CYCLE IN ANIMALS 
Certain cellular phenomena which concern the 
chromosome cycle have been described in preceding 
chapters and so need only be mentioned here. First, 
the occurrence of amitosis in the multiplication of 
the germ cells has an intimate relation to the speci- 
ficity of the chromosomes, since if nuclei divide en 
masse it seems improbable that the chromosomes be- 
come equally divided between the daughter nuclei 
(see Chapter V, p. 133) ; and second, the formation of 
nurse cells from ojgonia may be accompanied, as 
in Dytiscus (Chapter V, p. 120), by a chromatin- 
diminution process which may be regarded as a 
differentiation of mother germ cells into somatic 
cells (nurse cells) and odgonia, a differentiation re- 
sembling the segregation of the primordial germ 
cells in the cleavage stages of the egg. 
The most striking and perhaps the most important 
stages in the chromosome cycle occur during the 
growth and maturation periods of the germ cells. 
As briefly described and figured in Chapter II, 
the mitoses which occur during maturation are 
meiotic, since the mature germ cells have their chro- 
mosome number reduced one-half. The events in this 
process most worthy of our attention are those which 
take place during the stages known as synapsis 
and reduction. Wilson (1912) has summed up the 
questions that remain to be solved in the following 
words: ‘‘The cytological problem of synapsis and 
reduction involves four principal questions, as 
follows: (1) Is synapsis a fact? Do the chromatin- 
elements actually conjugate or otherwise become 
