174 LORANDE LOSS WOODRUFF. 



P. multimicronucleata, as the name indicates, characteristically 

 has many small micronuclei, usually from six to nine, the struc- 

 ture of which clearly resembles that of the micronuclei of P. 

 aurelia. The authors' figures show a general cell-form which 

 is more or less intermediate between that which is typical for 

 P. aurelia and for P. caudatiim. Powers and Mitchell emphasize 

 the persistence of the specific characters after conjugation. It 

 is an interesting form which warrants further study, especially 

 in view of the fact that we now know that reduplication of 

 micronuclei occurs during endomixis. 



In January, 1919, I isolated a ciliate, from an infusion of 

 fresh water and vegetable debris collected at New Haven, which, 

 though undoubtedly a Paramecium, showed characters that 

 distinguished it from any of the species hitherto described. It 

 has now been extensively studied in pedigree cultures for more 

 than a year and it has bred true. I have, therefore, definitely 

 designated it a new species, and named it Paramecium calkinsi 20 in 

 recognition of the fact that Professor G. N. Calkins of Columbia 

 University introduced students of the Infusoria to exact daily 

 isolation pedigree culture methods. Paramecium calkinsi pre- 

 sents an interesting composite picture of characters of P. aurelia, 

 P. bursaria, P. putrinum and P. trichium, with certain distinc- 

 tive ones of its own. 



The general body form of Paramecium calkinsi is more similar 

 to that of P. bursaria, P. putrinum and P. trichium than to that 

 of P. aurelia and P. caudatum. Indeed, at first glance, one is 

 reminded of P. bursaria, and further study suggests P. putrinum 

 and P. trichium because individuals in different stages of nutrition 

 and dividing at various rates exhibit quite a different appearance. 

 The form which is most characteristic in fact diagnostic when 

 the living cells are studied day after day in pedigree cultures is 

 given somewhat diagrammatically in Figs. I to 4- 21 



The cells of this pedigree culture of P. calkinsi, under favorable 

 food conditions, average about 120 /* in length and 50 /JL in 



20 L. L. Woodruff, "Paramecium calkinsi, sp. n.," Proc. Soc. Exp. Biol. & Med., 

 Feb., 1921. 



21 Drawings made by Miss J. E. Lovett of tins Laboratory. 



