118 



PROTOPLASMIC AGE OF PROTOZOA 



Subsequent observers have tried to straighten the tangle by giving new 

 terms for the different kinds of extranuclear material. Calkins ('04) 

 proposed the term protogonoplasm for the gamete-forming substance; 

 Goldschmidt ('04) proposed the terms "chromidia" and "sporetia" 

 for chromidia and "chromidial net" respectively, and Mesnil ('05), 

 the terms "trophochomidia" and "idiochromidia." Goldschmidt's 

 suggestion is a good one, but the term sporetia is not indicative of the 

 function, while Mesnil's term idiochromidia expresses the fate exactly 

 and will undoubtedly supplant the other names. In the present 

 instance the terms "chromidia" and "idiochromidia" will be used, 

 the former on grounds of priority, the latter on expediency. 



Fig. 46 



Arcella vulgaris. 



Secondary (gametic) nuclei (n) forming from the idiochromidia ch; 

 0, moutli opening of sliell. (After Hertwig.) 



(a) Idiochromidia Formation. — As might be expected, the method 

 of formation of the idiochromidia differs widely in the different types 

 of protozoa, and frequently in the same type. Although all methods, 

 in their final analysis, may be traced back to the same physiological 

 causes arising during this period of maturity, the dift'erent t}'pes may 

 be separated for purposes of description into three groups, as follows: 

 (a) Idiochromidia formation by nuclear transfusion; (5) by dissolu- 

 tion of nuclear parts; and (c) by nuclear fragmentation. 



Nuclear Transfusion. — This method of itliochromidia formation is 

 most characteristic of the rhizopods, and has been worked out mainly 

 in connection with arcella, centropyxis, difflugia, and other mono- 



