1914 ] Sharp: Diplodinium ecaudatum 95 



identical. D. cattanei was therefore the end member of the Diplo- 

 dinium ecaudatum series and as such was to be designated as D. ecau- 

 datum forma cattanei. This conclusion is materially strengthened 

 by the fact that no other five-spined Diplodinium has been described, 

 although several investigators have been working over this same field 

 since Fiorentini's (1889) first communication. Apparent discrepan- 

 cies between Fiorentini's figures and descriptions of Diplodinium 

 cattanei and my figure and description may be explained upon the 

 assumption that one of his figures (pi. 3, fig. 5) and his description 

 of the same was based upon an abnormal or pathological individual. 

 The possession of two contractile vacuoles is an exceedingly constant 

 characteristic of this species and, as a matter of fact, in his figure 4, 

 plate 3, Fiorentini pictures only two such vacuoles. The slight differ- 

 ence in size is easily accounted for when it is remembered that the 

 normal variations in the size of individuals of this group are consider- 

 able and that the natural tendency of the observer is to select the 

 larger and therefore more easily figured individuals. 



TABLE OF DIMENSIONS FOR ALL FORMS OF Diplodinium ecaudatum 

 Five animals in each case 



L. Length of body from mouth to anus in microns. 

 W. Width of body at level of micronucleus in microns. 



These measurements were taken from preparations which repre- 

 sented the average size. Exceptionally, preparations from other 

 stomachs were examined, in which all of the animals were either 

 undersized or oversized, thus suggesting the occurrence in Diplodinium 

 of races or pure lines similar to those described by Jennings (1909) 

 for Paramecium. 



OBSERVATIONS ON THE LIVING MATERIAL 



One of the first things that the observer notices when studying 

 these interesting little animals under conditions made as nearly normal 

 as possible is the terrific rate of speed at which they travel. Several 

 observations led to the conclusion that at the normal temperature, 



