270 BIOLOGY OF THE PROTOZOA 



which can no longer be discharged from the cell. This I interpret 

 as evidence of old age differentiation with the same fatal termina- 

 tion as that which follows highly differentiated gametes which fail 

 to unite in fertilization. 



In many organisms this physiological deterioration is accompanied 

 and manifested by structural degenerations. Maupas (1888) noted 

 the loss of micronuclei in old age ciliates as well as other degenera- 

 tions involving the motile organs (Fig. 130). The observations 

 have been fully confirmed with Uroleptus mobilis, particularly in 

 regard to to the loss of micronuclei, but also noticeable in the extreme 

 vacuolization of the protoplasm (Fig. 7, p. 28). In Paramecium 

 caudatum and in individuals which have not conjugated for a long 

 period, old individuals are characterized by hypertrophy of the 

 micronucleus and by the loss of trichocvsts in the cortex. 



Still another outcome of the physiological weakness is the ten- 

 dencv to divide abnormally, thus leading to monster formation. 



Fig. 138. — Paramecium caudatum monster, a type common at periods of old age. 



(After Calkins.) 



This has been typical of all old age cultures which have come under 

 my observation. Such monsters are strikingly like those formed as 

 a result of cutting Paramecium (see supra p. 264), but they never 

 grow into large amorphous masses of protoplasm which frequently 

 develop from mutilated Paramecium individuals (Fig. 138). 



The old age phenomena discussed above all involve a physiological 

 weakness or reduced vitality which may well be traced back to 

 increasing stability of protoplasmic substances, and lead to a 

 break-down in the protoplasmic organization. A fourth type has 

 to do with protoplasmic differentiations of a formative character 

 and involves structures which appear for the first time, and only, 

 when the protoplasm is old, probably as a result of the cumulative 

 differentiation which has taken place. The sporoducts of gregarines 

 furnish a good illustration of this phenomenon. Here in Gregarina 

 cuneata, according to Kuschakewitsch (1907), the old nucleus gives 

 rise to a minute germinal nucleus while the remainder is distributed 

 as chromidia throughout the cell. The characteristic sporoducts 



