230 GARY N. CALKINS. 



nize that a new species can no more be created on the basis of a 

 single cell or group of cells in the same stage of the life cycle than 

 a species of mammal can be established on the basis of a fore 

 limb, a jaw bone, or a tooth. It seems to me high time that the 

 science of protozoa-study should be freed from the charge of 

 dilettantism, and time for the literature to be cleared of the great 

 burden of synonyms that must ever increase so long as novices 

 in this field of study see and describe in print what to them are 

 new and curious forms. 



There is enough known at the present time of protozoan life 

 cycles to indicate that for a given species the cycle under similar 

 conditions is always the same, and we are justified in considering 

 the entire congeries of forms which the protozoon passes through 

 in its life cycle, and not the single cell, as the " individual," com- 

 parable indeed, as has long since been pointed out, to the meta- 

 zoon. There is nothing fanciful in comparing the rapid asexual 

 phase of a protozoon with the proliferation of somatic cells of a 

 metazoon, or the periods of conjugation and old age in a life cycle 

 with the sexual maturity and senescence in metazoa. So many 

 different forms are assumed by the protozoon in the numerous 

 stages of vitality, that, unless the entire cycle is known, even the 

 skilled observer might be justified in considering the various 

 phases of the same organism as different organisms. Instances 

 of this confusion come to your minds at once, and I need but 

 mention Plasmodium and Polymitus, Coccidium and Eimeria to 

 illustrate my meaning. The same confusion has recently come 

 under my observation in connection with Paramecium anrclia and 

 P. candatwn, which, since the classical work of Maupas, have 

 been generally but erroneously accepted as distinct species. 



The specific differences between these two supposedly different 

 forms have been emphasized by Maupas and Hertwig, and more 

 recently by Simpson, and are based upon some minor character- 

 istics of size and form but mainly upon the presence of two 

 micronuclei in P. anrclia and one in P. candatuiu. In all cultures 

 of/ 3 , caitdatiiiu, epidemics of conjugation appear at more or less 

 regular intervals. Four pairs of conjugating forms were isolated 

 from such a culture on March 11, 1905, and after separation the 

 eight individuals were isolated and their several histories followed 



