594 FERTILIZATION 



the chromidial origin of nuclei (Doflein, 1916). Kofoid (1921) says 

 "The evidence thus far presented of the de novo chromidial origin of 

 protozoan nuclei is wholly inadequate to establish this hypothesis." Intra- 

 cellular parasites are held responsible for some of the misinterpretations. 

 More recent investigations have clearly refuted at least some of the 

 earlier reports of the chromidial origin of nuclei. The reports of Myers 

 (1935, 1938) and of Le Calvez (1938) on Foraminifera are good ex- 

 amples of this. However, many other reports must be reinvestigated 

 before we can establish any very firm basis for our views. 



Calkins (1933, p. 70) points out that the chromidial net of Arcella 

 stains green with the Borrel mixture and usually gives a negative re- 

 action to the Feulgen treatment. This supports Hartmann's experiments, 

 in which the chromidia were dissolved out by pepsin, while the chromatin 

 of the secondary nuclei remained conspicuous. Belaf (1926) believes 

 this is conclusive evidence that chromidia are not composed of chromatin. 

 However, Calkins shows that by omitting the strong hydrolysis of the 

 Feulgen reaction, the chromidia are positively stained and therefore are 

 composed of chromatin, or at least that nucleic acid is present in them. 

 Nucleic acid becomes more concentrated in the nuclei, and this may 

 explain why the nuclei resist pepsin digestion while the residue is dis- 

 solved. The author can confirm Calkins's positive results in staining Ar- 

 cella chromidia with Feulgen. This organism has been stained with 

 Feulgen at many stages in its life history by omitting strong hydrolysis, 

 and intense staining of both chromidia and nuclei has resulted. 

 Chromidia are colored an intense purple in forms containing nuclei, 

 as well as in forms in which no detectable nuclei are present. It is not 

 impossible that in the latter forms, some of the larger chromidia are 

 actually minute nuclei which are lineal descendants by mitosis of the 

 original nuclei. 



According to Elpatiewsky (1907) and Swarczewsky (1908), the life 

 cycle of Arcella vulgaris is extremely complicated. In addition to several 

 methods of asexual reproduction, both chromidiogamy and anisogamous 

 syngamy occur. In chromidiogamy two Arcella, the nuclei of which are 

 degenerating into chromidia, come together. The protoplasm of one 

 passes over into the shell of the other and, after the intermingling of 

 the chromidia, half of the protoplasm passes back into the first shell, 

 and the two organisms pull apart. After separation, the chromidia of 



