HEREDITY IN THE PROTOZOA 283 
missing parts. Should one end happen to have 
some local peculiarity or abnormality, this may be 
“inherited” through that half, but not by the other 
half. The abnormality may be said to be persistent 
rather than to be inherited. 
Fission of protozoa is generally compared with 
cell-division in the soma of higher forms. It is 
known that here the two daughter-cells receive the 
chromosome complex of the mother cell and usually 
like parts of the maternal cytoplasm. When, as 
often occurs in early embryonic cells (blastomeres), 
the two daughter-cells get very different proportions 
of the visible inclusions of the original parent cell 
(such as pigment, or yolk) it has been shown by 
centrifuging experiments that such inclusions do not 
have a differentiating influence on the cells that 
contain them. Embryonic differentiation might 
however be influenced by other materials laid down 
regionally in the egg and not displaced by centrifug- 
ing. So far as known, such materials would have 
no permanent effect upon inheritance unless they 
were of a plastid character and capable of inde- 
pendent multiplication. It is customary, therefore, 
to consider all daughter cells as inheriting the entire 
genetic complex of the mother cell, and differ- 
entiation is ascribed to other influences than to 
sorting out of hereditary materials. It is referred 
to the environment in the widest sense, including 
the relationship (physical and chemical) to neigh- 
boring cells, and to the external surroundings of 
the whole embryo. 
