OPALINID CILIATE INFUSORIANS — METCALF 



487 



being demarcated by a furrow at its base from the rest of the posterior 

 end of the body. This is an intermediate condition between the 

 "species" uruguayensis and antunesi. I am describing it as a form of 

 Z. uruguayensis. 



Measurements, ia microns: 



Nucleoli 6. 



The form quadrata, with the same general measurements, is found 

 also in Bujo crucifer. 



ZELLERIELLA ANTUNESI Pessda 



Figures 42, 43 



Hosts: Leptodactylus ocellatus (Linnaeus), Bufo crucifer Wied, B. 

 dorhignyi Dumeril and Bibron, and B. arenarum (Hensel). 



In these four hosts at Rio de Janeiro and at Montevideo there are 

 Zelleriellas that it is difficult to distinguish, for after study of many 

 infections one realizes that they 

 seem to grade into one another. 

 One form, Z. antunesi, is astonish- 

 ing. It is usually quite distinct, 

 but in a few infections its most 

 distinctive character, the remark- 

 able taU, is but little developed. 

 When the tail is in the usual con- 

 dition, the body of the animal is 

 almost double, consisting of a 

 lower portion without tail and a 

 second upper portion fused in front 



with the lower, but becoming more and more elevated behind, until at 

 the back of the body it forms a high, narrow ridge, which is drawn out 

 to a cylindrical, pointed tail projecting upward and backward to a 

 distance almost equal to half the length of the body. Study of individ- 

 uals in which the tail is developed to varying degrees, especially those 

 infrequent individuals in which it is almost rudimentary, shows that 

 in its fundamental morphology the tail is the posterior point that 

 occurs in many species of all four genera of opalinids. It will be 

 discussed later. 



Figure i2.—Zellerietta antunesi Pessoa: a—c, From 

 Bufo crucifer; d, from Leptodadvlus ocellatut. All 



xn7. 



