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Wager . — The Life-history and 
nuclei remain visible through all the subsequent stages of development 
either at the periphery of the chromidial mass or slightly embedded in it. 
The presence of these well-marked chromidia in Polyphagus recall so 
strongly the appearances presented by the cells of many Protozoa that 
I propose to discuss very briefly the present state of our knowledge of 
chromidia. 
Chromidia. 
Hertwig (’02) designated as chromidia the discrete chromatin, derived 
from the nucleus, which is found in the form of granules or more or 
less branched strands or networks in many Protozoa. They were first 
recognized in Actinospherium , in which they occur abundantly during 
particular states of metabolism, as in over-feeding or starvation. 
The occurrence of diffused chromatin in the cell, and the occasional 
disappearance of all other traces of nuclei, suggested to Hertwig that 
in certain organisms the diffused chromatin might entirely replace the true 
nucleus. This is probably the case in the Bacteria and Cyanophyceae. In 
these forms the nucleus as a histologically defined organ is wanting, but 
chromatin in the form of chromidia is diffused through the cytoplasm. 
At the present time a good deal of confusion exists as to the precise 
nature and significance of chromidia. Many authors regard all deeply 
stainable granules in the cytoplasm, whether derived from nuclei or not, as 
chromidia, in which case the term has no real significance, and certainly not 
the significance which, if I understand him correctly, Hertwig meant 
to convey when he first made use of the term ‘ chromidien \ The term 
chromidia should, in my opinion, be strictly reserved for those granules that 
can be shown to have been derived from nuclei or which take the place of 
the nucleus. The singular of chromidia is chromidium, which obviously 
means a single granule, and not the mass of granules to which it has been 
applied by some observers, in a manner which strikes me as very confusing 
(cf. Minchin, 1912, p. 65). Minchin suggests the term chromidiosomes for 
the separate particles which Hertwig called chromidia, but it seems to me 
that this is unnecessary if we use the original term properly in Hertwig’s 
sense. 
So far, it appears that four distinct categories of chromidia can be 
recognized : 
1. Those which definitely represent the nucleus of the cell and are the 
only nuclear structure present. Such occur in some Bacteria and possibly 
Cyanophyceae. 
2. Those which are formed at certain stages in the life of a cell by 
the breaking up of a nucleus into granules, which are distributed in the 
cytoplasm, but which are capable of being re-formed into nuclei. These 
may be found in some Protozoa. 
3. Those which are extruded from the nucleus for the purpose of 
