116 



PROTOPLASMIC AGE OF PROTOZOA 



The first definite observations upon chromidia formation were 

 made by Hertwig ('99) in connection with the minute structure of the 

 shelled rhizopod Arcella vulgaris. Previous observers had noted that 

 chromatin-like granules are distributed throughout the cell body in 

 many of these types, but Hertwig was the first to describe the origin of 

 this material from the nucleus in arcella and to show that it forms a 

 dense zone of granules in the protoplasm (Fig. 44). At that time 

 Hertwig described this material under the name of "chromatin net," 

 but later, in 1902, he called it the "chromidialnetz," because of the 

 reticulate structure assumed by the granules en masse. The function 

 of this extranuclear chromatin was not made out, however, until the 

 following year, when Schaudinn ('03) worked out the origin and fate 

 of similar masses of granules in several different kinds of sarcodina 



FIG. 43 



"Chromidia" in rhizopods. Arcella vulgaris (on left) and Ameba proteus (on right). 

 dark granules are the idiochromidia distributed throughout the cytoplasm. 



The 



(Polystomella crispa, Centropyxis aculeata, Chlamydophrys siercorea, 

 and Entameba coli) and found that the nuclei of the conjugating 

 gametes were developed solely from this extranuclear chromatin. He 

 thus 'interpreted the material of the chromatin net of arcella and its 

 allies as sexual or racial chromatin and correctly compared it with the 

 micronuclei of the infusoria. 



In the meantime the subject became more complicated by Hertwig's 

 further observations upon extranuclear chromatin in the heliozoon 

 Actinospherium eickhornii. These observations, first noted in 1897, 

 were confirmed and extended in 1904, when it was shown that in 

 starving forms and as well in forms that had been overfed, the nuclei 

 all disintegrate and the chromatin contents becomes distributed 

 throughout the cell body (Fig. 45). The distributed chromatin thus 



