i8 3 
Cytology of Polyphagus Euglenae. 
metabolism and are finally used up and not reabsorbed into the nucleus or 
reconstructed into nuclei. They are found in egg-cells of various kinds and 
probably to some extent in all cells in active growth and division. The 
chondriosomes and chromatin structures of similar nature derived from 
nuclei would also be included here. 
4. Those which are extruded from the nucleus, or cut off by division 
for purposes of metabolism and vegetative growth, but which are at once 
constituted into nucleu's-like structures more or less clearly defined in the 
cytoplasm. The macro-nuclei of Protozoa, the granular structure of Poly- 
phagus , and possibly the so-called coenocentra and perhaps pyrenoids are 
instances. 
So far as their functions are concerned, we thus see that we have two 
main types of chromidia, one possessing a purely vegetative function, and 
the other a generative or reproductive function. The following table shows 
the general relationship of the four categories given above : 
CHROMIDIA 
Generative chromidia Vegetative chromidia 
1 j 
1 2 3 4 
Those which replace Those which are cap- Extruded for metabolism Those which accumulate 
the nucleus. able of being re- and remain diffused in in nuclear-like struc- 
formed into nuclei. the cytoplasm. tures. 
Goldschmidt (’ 04 ) proposes the terms chromidia and sporetia for the 
vegetative and generative chromidia respectively, and Mesnil (’ 05 ) suggests 
trophochromidia and idiochromidia. Minchin (p. 150), however, considers 
that the term chromidia should be retained ‘ to denote simply extranuclear 
particles of chromatin, and to qualify the term by the adjectives vegetative 
and generative when required These terms are sufficiently distinctive, but 
it must not be forgotten that those chromidia which definitely replace the 
nucleus, as in Cyanophyceae and Bacteria, have both generative and 
vegetative functions. 
In Polyphagus, the granular mass which we regard as chromidial arises 
from the nucleus, and is definitely extruded for purposes of metabolism. 
In the zoospores and in the early stages of the development of the thallus 
this chromidial mass is homogeneous or finely granular (Figs. 48, 54). 
Later, it exhibits a vacuolated structure, owing to the formation of globules 
of oily substance in the alveoli (Fig. 55). This fatty substance, which 
is formed as a reserve food material for use during subsequent growth and 
development, appears to be produced largely at the expense of the 
chromidia. 
Chromidia are present at all stages in the life-cycle of Polyphagus , and 
are constantly being reinforced, as they are used up, by fresh extrusions 
from the nuclei at various stages in the nuclear cycle. The granules found 
