Studies on the Life History of Protozoa. 45 1 



The surest evidence of what may be considered old age 

 in this form, was therefore, functional, and was expressed by 

 diminished division rate and by the increased frequency of ab- 

 normal binary fission. Abnormal division, as a matter of fact, 

 like nuclear hypertrophy, may occur at all periods and marks 

 some particular weakness of the single individual; occurring more 

 frequently, however, at certain periods of depression, such ab- 

 normalities give evidence of general protoplasmic weakness. 

 The various types of incomplete division are very instructive and 

 a more prolonged study than I was able to give to them might 

 afford positive evidence of the nature of the pathological changes 

 involved. In some of the specimens which T obtained during 

 periods of depression, the macronuclei and micronuclei appear 

 normal; in others there is a macronucleus in each of the daughter 

 individuals, but the micronucleus is undivided; in others the 

 macronucleus is divided but remains in one individual, the micro- 

 nucleus is undivided and remains with the original macronucleus, 

 while the daughter individual has no trace of nuclei. In all cases, 

 finally, of pathological division the cortical plasm appears ab- 

 normal and vacuolar, while the endoplasm is very frequently 

 disintegrated and abnormal (Figs. 25 and 26). 



While these observations are too few to permit far-reaching 

 conclusions, they are sufficient to indicate that some protoplasmic 

 changes have taken place, and further, that the cortical plasm has 

 become modified in some way. Indeed, the inability completely 

 to divide may be accounted for by the loss of vitality in this par- 

 ticular part of the protoplasm, for in the majority of cases the 

 initial stages of division are safely passed, the final separation 

 alone being retarded and usually omitted altogether, so that 

 monsters of three or four individuals may be formed through the 

 continued incomplete division of the original degenerate specimen 

 (Fig. 25). As is well known, the cortical plasm is the seat of the 

 myoneme formation, of the cilia, and of other motile organs, and, 

 in general, may be said to possess kinetic or motor functions. 

 That this portion of the protoplasm is subject to change is shown 

 by the fact that at certain times the outer protoplasm becomes 



