8o 



HE BIOLOGY OF STENTOR 



from the circumference of the cell produce grossly unequal 

 daughters, not accounted for by the relatively small loss of cyto- 

 plasm. Enlarging upon an experiment by Weisz (1951b), I found 

 that if the mouthparts or the membranellar band or both are 

 minimally excised or caused to be shed by salt treatments from 

 early dividers, proters are later produced which are only about 

 half the volume of the opisthes (Fig. i8a). That this difference is 

 too great to be due to the ablations alone is obvious, and confirmed 



Fig. 17. Predivision of carbohydrate reserves (S. coeruleus). 



A. Normal distribution of glycogenoid granules in a 

 subcortical band at the posterior end, open in the primordium 



meridian. 



B. Separation of granules into two groups at stage 5, the 

 posterior border of the anterior aggregation precisely coinciding 

 with the future fission line and the posterior granules somewhat 



diffuse. 



C. Division leaves about half the carbohydrate reserves in 



each cell. (After Tartar, 1959a.) 



by the fact that such operations on dividing animals at stages 5 and 

 6, when the division line is already determined, do yield products 

 which are approximately equal. It therefore appears that such 

 interferences have a marked effect on whatever determines the 

 level of the fission line, shifting it far forward from its usual 

 position. A rare case of division in a fusion complex of parts of 

 two stentors suggests that the fission line may also be laid down 

 far posterior of its normal location (Fig. i8b). 



