t^8 THE BIOLOGY OF STENTOR 



varies in degree of polymerization along the nuclear chain. Faure- 

 Fremiet and Rouiller speak of this DNA as in the form of micro- 

 somes. In dark-field illumination I have found that the exposed 

 macronuclear nodes are often a glow^ing light blue, which may 

 indicate something of their composition or state as aifecting the 

 scattering of light. 



The micronuclei of stentors were first described by Maupas 

 (1879) and later by Johnson (1893). These very small nuclei 

 reside on or near the macronuclear chain. Multiplying mitotically, 

 they are typically chromosomal, as further substantiated by their 

 behavior during conjugation (see p. 329). 



7. The endoplasm 



The interior cytoplasm w^as examined by Weisz (1949a) who 

 found that it did not stain with basic dyes and only diffusely with 

 acidic. Neutral red was taken up by the living coeruleus and stained 

 various inclusions so that stentor may be said to have a 'Vacuome" ; 

 this dye was segregated by the contractile vacuole. Chromidial 

 nets and metachromatic volutin granules were not present. 



By introducing minute electrodes into the cell, Gelfan (1927) 

 went to much trouble to prove that the electrolyte concentration 

 in Stentor is higher than that in the surrounding fresh water medium, 

 a conclusion which could have been inferred from the pulsation 

 of the contractile vacuole in voiding water imbibed through 

 osmosis. The specific conductance was lower in stentors than 

 in three other ciliates tested. Internal conductivity decreased with 

 injury, presumably due to the leakage of electrolytes from the cell. 



The endoplasm of stentors presents a foamy appearance which 

 was first emphasized by Butschli in keeping with his theory of the 

 alveolar nature of protoplasm. Correspondingly, Randall and 

 Jackson found by electron microscopy that the endoplasm con- 

 sists of numerous vacuoles within a matrix which shows many 

 small particles and vesicles. An endoplasmic reticulum was not 

 revealed. The vacuoles have a definite membrane and seem to be 

 especially numerous in the sub-cortical regions. Within the endo- 

 plasm are also found typical protozoan mitochondria. Randall and 

 Jackson (1958) found them to be Janus green B positive and 

 having triple membranes of equal width, if one counts the material 

 between outer and inner layers as the third. The enclosed tubular 



