The Life-History of Hypotrichous Infusoria. 613 



during depression periods and the very similar morphological 

 changes which occur in the hypotrichs studied, justifies, I believe, 

 the assumption that the power of assimilation becomes diminished 

 as the culture proceeds and that the effect of the beef-extract is 

 essentially that of concentrated nutrition, resulting in the rapid 

 assimilation of the salts, etc., necessary for the continued life of 

 the animal. 



It has been customary to regard the macronucleus as relatively 

 vegetative in function and the micronucleus as reproductive; and 

 this accords well with the results of these experiments, in so far as 

 the morphological variation of the macronucleus may be regarded 

 as an indication of the apparent lack of assimilation of the food 

 taken. Throughout the culture no form-changes were apparent 

 in the micronuclei themselves, but they showed a tendency to 

 numerical reduction when the fission-rate was at the highest, 

 and to reduplication when the lowest rate of multiplication ensued. 

 This may be explained by supposing that the exceedingly rapid 

 rate of assimilation, calling for such frequent bipartitions, results 

 in the exhaustion of the micronuclei during these periods; but 

 when assimilation is at a low ebb, the little demand for the dynamic 

 forces of the cell results in the reduplication of the micronuclei 

 beyond the typical number. Thus Maupas's observations that 

 in certain hypotrichous forms the micronuclei are reduced in 

 number, and later appear again in greater number, is entirely 

 substantiated by these cultures. Variations in the number of 

 micronuclei is not unknown in other forms. Johnson ('93), for 

 instance, working on Stentor, found that from one to eight may 

 be associated with each node of the macronucleus. However, 

 the disappearance of all the micronuclei in certain forms, as 

 described by Maupas, has never occurred in my cultures, and 

 the continuance of his series for many generations without this 

 cell-organ I believe is open to question. 



Whatever may be the correct interpretation of the nuclear 

 changes taking place in the life-history of the hypotrichida, these 

 cultures strongly suggest that it is customary to regard the struc- 

 ture most frequently observed in "wild" Infusoria as too fixed in 

 character, and to overlook the fact that under varying condi- 

 tions, modifications may occur which are in no way abnormal. 

 Biitschli ('83) comments on the frequent presence of a coarsely 

 alveolar or vacuolar structure of the protoplasm of certain ciliates 



