author's abstract of this paper issued 



BY THB bibliographic SERVICE, OCTOBER 28 



UROLEPTUS MOBILIS, ENGELM. 



I. HISTORY OF THE NUCLEI DURING DIVISION AND CONJUGATION 



GARY N. CALKINS 

 Columbia University, New York City 



NINETY-FIVE TEXT FIGURES 



Uroleptus mobilis is a rare hypotrichous ciliate first described 

 by Engelmann ('62) and apparently not recognized since then, 

 for I find no further description of it in any of the more important 

 contributions to taxonomy of the Infusoria. 



In October, 1917, the organism appeared in considerable num- 

 bers in an old hay infusion that had been standing for several 

 months in the zoological laboratory of Columbia University. 

 It was successfully cultivated, and abundant material for study 

 of all the unportant phases of the life history was secured. 



Engelmann's description of Uroleptus mobilis is as follows: 



Body form constant; plastic; circular in section; about 12 times longer 

 than broad; tapering gradually to a broadly pointed posterior end. 

 Lateral cilia equally long throughout. With six elongate nuclei. This 

 species, which came from the Boticzbach near Prag, is distinguished 

 from the other species of Uroleptus recently described by Stein, by the 

 constant presence of six nuclei arranged one behind the other. It 

 stands close to Stein's Uroleptus rattulus but, unlike this species, it 

 possesses no sharply pointed posterior end, and the lateral cilia are 

 equally long on the tail and body. The adoral row of cilia (adoral zone) 

 occupies about one-ninth of the total body length, with an undulating 

 membrane fastened on its inner side; a peristome field appears to be 

 entirely absent, or at least extremely narrow. Whether, as in other 

 Uroleptus species, two longitudinal rows of fine ventral cilia are present, 

 I could not make out since the animal is very lively and inclined to 

 creep about, snake-like, between plant remains. Our species, more- 

 over, which appeared in great numbers, measured on the average, 0.30 

 mm. All specimens were about of the same size. Division was not 

 observed. (Loc. cit., p. 386.) 



The essential characteristics here are the elongate cylindrical 

 body with circular section, the frontal cirri, the equally long 



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