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 foe All Forms of Diplodinium ecaudatum 

 Five animals in each ease 



Animals ecaudatum 

 measured L. W. 



caudatum 

 L. W. 



bicaudatum 

 L. W. 



tricaudatum 

 L. W. 



quadri- 



caudatum 



L. W. 



cattanei 

 L. W. 



1st 



122 



40 



122 45 



126 



44 



126 



46 



138 



52 



138 



53 



2nd 



132 



45 



126 45 



122 



42 



122 



42 



112 



38 



126 



46 



3rd 



126 



44 



132 48 



126 



45 



132 



45 



138 



54 



132 



52 



4th 



132 



45 



132 50 



130 



48 



132 



48 



138 



54 



138 



54 



5th 



122 



43 



138 53 



126 



45 



138 



45 



132 



50 



122 



44 



Average 



127 



43 



130 48 



126 



45 



129 



47 



131 



50 



131 



50 



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, 



