Studies on the Life History of Protozoa. 445 



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 were rescued 

 only with the greatest difficulty by the use of pancreas extract. 

 Figs. 8, 9 and 10 represent individuals that had been in extract of 

 pancreas for 48 hours, and then transferred to hay infusion. They 

 are identical, therefore, with the individuals that lived and carried 

 the race to the 742d generation. In these forms the endoplasm 

 in most cases is normally vesicular in the center and gastric 

 vacuoles are common, while the ends alone still retain the dense 

 granular aspect. 



From this time until the race died out the division rate was 

 sluggish. The conditions of the protoplasm in the later individ- 

 uals was decidedly characteristic (Figs. 17, 19, 20, 21 and 22). 

 Throughout the fall, individuals would appear with densely granu- 

 lar protoplasm, which is invariably the sign of death, unless the 

 animals are stimulated in some way. In such forms the macro- 

 nucleus may or may not be normal, whereas the micronucleus as 

 a rule becomes hypertrophied and the ectoplasm full of great 

 vacuoles. Fig. 22 is a good representation of the conditions 

 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 chro- 

 matin. 



The sister-cell of the one pictured in Fig. 22, and 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 was a row of dorsal feeding canals, such as those 

 characteristic of the more generalized holotrichida {e.g., Chlamy- 

 dodontida:). The rest of the body contained eight or ten large 

 vacuoles not contractile. The macronucleus was slightly hyper- 

 trophied, and visible, indicating the approach of disintegration. 



