SOME PROBLEMS OF REPRODUCTION. 57 
advance, are only evenly distributed between the daughter- 
cells. This obviously, as stated, is only another way of dis- 
tributing the segments formed. If in the schema B, C, repre- 
sent two of the chromatomeres of the gametogonial nucleus, 
B', C'1—B’, C?, those produced by their splitting, and the 
dotted lines the cell divisions, we see that the sole difference 
needed to change this into a schema of ordinary cell division 
would be to prolong the middle dotted line back to the level of 
B!, C1—B!, Cl}. 
B2, C2 
BE OK Bt Soi eee line of second fission (absent in 
ye 18) (OF female of Ascaris). 
i CGe Ws Wie i a aca acre ens line of first fission (formation of 
\ pes C? first polar body in female). 
BE TS Satoh ate ard ate line of second fission (formation of 
‘BC? second polar body in female). 
Fie, 10.—Schema of modified mitosis in gametogeny of Ascaris megalo- 
cephala bivalens. 
A misinterpretation of these facts has led to a belief that 
the reduced number of chromatomeres in gametes was due to 
the removal of half of them, or that a true transverse division 
of chromatomeres replaced the ordinary longitudinal splitting. 
A complete hypothesis to explain this reduction is certainly 
premature when we know practically nothing of the numerical 
relations of the chromatomeres in Protozoa and any (save one) 
Cryptogams. We may, perhaps, regard it as an adaptation to 
prevent an undue multiplication of chromatomeres in the 
zygote, and the cells produced therefrom. The halving 
cannot be essential, for the reduction is only by one third in 
many plants. The reduction itself cannot be essential, for 
it is absent in some plants, and an augmentation probably 
occurs in the cases where the gamete possesses a fusion nucleus, 
as well as in Muscari. Hence all theories of gametogeny 
and fertilisation based on the assumption that this reduction 
is universal or uniform must fall to the ground. 
We must remember the fact that the reduction takes place 
in the pollen-mother-cells of Flowering Plants, which are them- 
selves homologous with the mother-cells that form tetrads of 
