278 J. F. McClendon 



cannot be permanently changed without the formation in it of 

 one or more new chemical substances. In other words we might 

 hypothetically consider the horn alluded to as of the nature of a 

 graft differing chemically from the Paramoecium to which it was 

 attached. 



4. ON VARIATIONS IN PARAMCECIUM CAUDATUM AND P.AURELIA^ 



In making the foregoing studies I was interested in inquiring 

 into the identity of the species used. In the experiments at 

 Ashland, Va., only one form was used. It had but one micro- 

 nucleus and agreed in other respects with descriptions of Para- 

 moecium caudatum. At the University of Missouri two forms 

 were found, one similar to that studied in Virginia and another 

 having two micronuclei, and in this respect agreeing with descrip- 

 tions of Paramoecium aurelia. Calkins ('06) found a case of 

 P. caudatum acquiring two micronuclei and some of its offspring 

 losing one micronucleus and becoming normal P. caudatum 

 again. He further states that the number of micronuclei is the 

 only invariable character for separating caudatum from aurelia 

 and therefore they are probably the same species. Whether 

 caudatum and aurelia form two species or not cannot be decided 

 from the data at hand but I have evidence to show that these two 

 forms are quite distinct. In none of the numerous cultures which 

 I have kept for months and in one case a year, have I found indi- 

 viduals with different numbers of micronuclei in the same culture. 

 No characters of outward form were found that would serve to 

 separate caudatum and aurelia. The size character is best studied 

 in graphs of the lengths of a large number of individuals of each 

 culture (Fig. 10). In each curve in Fig. 10 the lengths of the indi- 

 viduals measured in fractions of a millimeter are plotted as abscis- 

 sas and the number of individuals in a class represented by arbi- 

 trary units on the ordinates and marked at the top by a cross. 

 The curve itself is merely to aid the eye in comparing measure- 

 ments from one culture with those from another, as are also the 



* These observations were made at the University of Missouri. 



