l8o LORANDE LOSS WOODRUFF. 



species presents a complex mosaic of the characters of the other 

 members of the genus 26 indeed the intrageneric relationships 

 of the new species are its chief interest. 



A survey of the six species of Paramecium under discussion 

 shows that they fall into two quite clearly defined groups which 

 may be referred to as the 'aurelia group' and the 'bursaria 

 group' respectively. The members of the 'aurelia group' 

 (P. aurelia, P. caudatum and P. multimicronudeata) are charac- 

 terized by a relatively long spindle- or cigar-shaped body; 

 those of the 'bursaria group' (P. bursaria, P. putrinum, P. 

 trichium and P. calkinsi) by a somewhat shorter and broader 

 form, with a tendency, especially prominent in P. bursaria, 

 toward a dorsoventral flattening. 



Within each of these groups are found two general structural 

 types of micronuclei. One type, which may be termed the 

 'caudatum type,' is exhibited by P. caudatum in the 'aurelia 

 group,' and by P. bursaria, P. putrinum and apparently by 

 P. trichium in the 'bursaria group.' Though Stokes' figure 

 of the micronucleus of P. trichium leaves much to be desired, it 

 clearly indicates that the single micronucleus is not of the 

 'endosome' type. The other type of micronucleus, the 'endo- 

 some' or 'aurelia type,' occurs in P. aurelia and P. multimicro- 

 nudeata in the 'aurelia group,' and in P. calkinsi in the 'bur- 

 saria group.' All species with the 'caudatum type' character- 

 istically possess one micronucleus, and those with the 'aurelia 

 type,' two micronuclei, except P. multimicronudeata in which 

 the number apparently varies from six to nine. 



Paramecium calkinsi represents the 'aurelia type' of micro- 

 nuclear apparatus in the 'bursaria group' of species. It is 

 possible that future study may show that certain of the para- 

 mecia under discussion (e.g., P. micronudeata, P. trichium, P. 

 putrinum) should be regarded as racial forms rather than 

 distinct species, but I believe that the data presented above 

 indicate beyond doubt that Paramecium calkinsi takes its place 

 by P. bursaria, as Paramecium aurelia has by P. caudatum, as a 

 distinct species. 



!6 It is unnecessary to illustrate the cell form and micronuclear structure of the 

 several species of Paramecium because figures are available in many of the mono- 

 graphs cited. Especial reference should be made to the figures given by Jennings 

 and Hargitt, Schewiakoff, and Hamburger. 

 March 4, 1921. 



