MORE COMPLICATED LIFE CYCLES 129 



divisions were frequent. Toward the end of June, however, when the 

 A series nearly died out in the 620th generation, the conditions were 

 very different. Fig. 26, left, is from a specimen in the 615th generation; 

 its size is below the normal; its endoplasm is choked up with granules, 

 and there is no trace of vacuoles save the contractile vacuole near one 

 end. The macronucleus is definitely granular, and its contour is 

 irregular, as though devoid of nuclear membrane. The micronucleus 

 is elongate and spindle-formed. The ectoplasm is not deformed, and 

 save for the absence of trichocysts it appears to be normal. This was 

 the condition of the protoplasm when the usual large number of culture 

 individuals was reduced to 6 A's and no B's, and a condition from 

 which the A series was rescued only with the greatest difficulty by the 

 use of pancreas extract. 



"From this time until the race died out the division rate was slug- 

 gish. The conditions of the protoplasm in the latter individuals was 

 decidedly characteristic. Throughout the fall individuals would 

 appear with densely granular protoplasm, which is invariably the 



FIG. 54 



* 



Paramecium aurelia from culture in 741st generation. The macronucleus and endoplasm 

 are normal, the micronucleus is abnormal, and the cortical plasm is filled with vacuoles. 

 (After Calkins.) 



sign of death, unless the animals are stimulated in some way. In such 

 forms the macronucleus may or may not be normal, whereas the 

 micronucleus, as a rule, becomes hypertrophied and the ectoplasm 

 full of great vacuoles. Fig. 54 is a good representation of the condi- 

 tions at this time. The endoplasm is apparently normal; there are 

 food vacuoles and endoplasmic granules and vesicular structure, but 

 the micronucleus is spherical and vesicular, has lost its usual place 

 in a niche in the macronucleus, and shows evidence of granular 

 modification of the previously homogeneous chromatin. 



"One of the two oldest of the A series (742 generations) showed 

 the following points while alive: 'A12 was alive this morning and was 

 picked out for examination. It had two contractile vacuoles situated 

 dorsally and close together. The astral canals were absent; in their 

 place w r as a row of dorsal feeding canals, such as those characteristic 

 of the more generalized holotrichida (e.g., Chlamydodontidci). The 

 rest of the body contained eight or ten large vacuoles not contractile. 

 The macronucleus was slightly hypertrophied and visible, indicating 

 9 



