234 THE PROTOZOA 



It is a significant fact, first pointed out by Maupas ('89), that 

 micronuclei in Infusoria which have about exhausted their potential 

 of vitality, disappear by atrophy and absorption in the cytoplasm, 

 while the latter continues to live and even to divide for a limited 

 time (e.g. Onychodromus). Thus, the loss of vitality operates upon 

 the nucleus as upon the remaining protoplasm, and the final divi- 

 sions of the nucleus, like the final divisions of the cells, result 

 in daughter-nuclei, which have not the power to live, and which 

 disappear in the cytoplasm. Furthermore, if two individuals can 

 fuse only when the body protoplasm is in the proper condition (Dif- 

 fltigia, Amceba, etc.), the same may be true of nuclei. It is certainly 

 true that nuclei of the plasmodia of Mycetozoa, or of Actinophrys in 

 plastogamy, or of adult multinuclear Actinosphceria, do not fuse. 

 But when two Difflugias are in the proper condition for conjugation, 

 the nuclei do fuse. When, however, two individuals are in the 

 proper condition, 'so far as the cytoplasm is concerned, it does not 

 follow that the nuclei are ready, and each nucleus may undergo 

 division prior to fusion, one of the daughter-nuclei disintegrating 

 and disappearing (Monocystis, Actinophiys\ or several of them 

 disappearing (Infusoria, Actinosphatium). In Coccidiida a certain 

 amount of the nuclear material is budded off and disintegrates while 

 in the plasm, and the conjugating nuclei, without membranes, fuse 

 to form the cleavage nucleus. Such cases may be interpreted as 

 evidence of loss of vitality to such an extent that the rfucleus has the 

 power to divide, but not to stimulate division of the cell-body. 



The loss of vitality is, I believe, the principle which lies at the 

 bottom of the so-called maturation-phenomena among the Protozoa. 

 Briefly reviewing some of these processes in Protozoa, it will be seen 

 that in some cases, as in senescent Infusoria, the nucleus atrophies, 

 while in other cases the nucleus divides once or twice previous 

 to fusion, thus simulating the maturation of Metazoa. The former 

 has been observed in Euglypha and Actinosphcerium, the latter in 

 Actinophrys, Actinosphczrium, some Coccidiida, and in Infusoria. 



In Euglypha, Blochmann ('88) observed the conjugation of two 

 individuals, which had become united by their mouth parts. The 

 cytoplasm of one conjugant passed into the shell of the other and 

 fused with the cytoplasm there, but the nucleus was left behind. A 

 pseudopodial process from the fused cytoplasm finally picked up the 

 rejected nucleus, and its position in the cytoplasm was restored. It 

 did not live, however, to fuse with the other nucleus, but disintegrated 

 in the plasm (Fig. 129). These observations have been recently 

 confirmed by Prowazek ('oo) and are regarded by Biitschli and 

 Blochmann as an indication of reduction previous to conjugation; but 

 it may be interpreted as an instance of degeneration of the nucleus, 



