296 



GARY N. CALKINS 



The contractile vacuole is single, spherical, and lies in the 

 center of the body near the dorsal surface. 



The protoplasm is dense and alveolar with few granules in the 

 endoplasm, but with many refringent granules forming a heavy 

 granular coating in the cortex. These granules may possibly 

 be mitochondria, although the mitochondria methods have not 

 been used to determine this point. They are spherical in the 

 ordinary vegetative stages, but are drawn out into rods which^ 

 divide transversely during division stages. 



The length of vegetative fonns varies from 140 to 165 m, and 

 the diameter at the center of the body, from 11 to 17 m- 



The cysts are spherical and the cyst wall smooth with an 

 average diameter of 32.7 m- 



While Engelmann's species averages 300 n in length, the present 

 fonn averages only 158 n in the normal vegetative condition. 

 The dividing and conjugating stages are much shorter, but 

 have a larger diameter. These measurements are shown in the 

 accoirpanying table: 



Vegetative stages. . 

 Division stages. . . . 

 Conjugation stage- 



AVERAGE 

 LENGTH 



158.6 JU 



99.0 m 

 105.2 m 



AVERAGE 

 DIAMETER 



15 m 

 30 m 

 15 m 



EXTREMES 



146 M-168 M 

 93m-115m 

 85 M-120 M 



A second variation from Engelmann's species is the number of 

 macronuclei. While in the earlier description six macronuclei is 

 given as the invariable number, in the New York variety the 

 number is eight, six being found, in only one individual out of 

 many hundreds examined; nine, ten, eleven, and even twelve 

 macronuclei are found more frequently than six. 



A third variation is the position of the contractile vacuole 

 which lies in the center of the body and not in the anterior third. 



These variations are not important enough to warrant a new 

 species of Uroleptus; they are consistent and permanent, how- 

 ever, and justify the belief that the present organism is a new 

 and a well-marked variety of Uroleptus mobilis. 



