Opalina. Oly 
Opalinae dimidiatae having the posterior end of the body pointed. 
ZELLER Was uncertain whether to regard these stocky individuals 
as Opalinae dimidiatae of a peculiar form, or as belonging to a new 
species. 
Detace & Herovarpd (1896), without having seen these Opalinas. 
interpreted ZELLER’s figure as indicating the presence of vestigial 
excretory organs, an interpretation which I have shown to be 
mistaken (Mercaur 19086). 
NERESHEIMER (1907) again found these peculiar Opalinae in 
Rana esculenta, and, without adding to ZeLuEr’s description, gave 
them the name 0. zelleri, believing them to belong to a distinct 
species. 
In the same year I independently (but later) gave them the 
same name, it being only natural to name them after their discoverer. 
I have seen these forms but twice, ZELLER apparently saw 
them several times, though he does not say definitely. In both 
instances when I saw them they were with Opalinae which un- 
doubtly belonged to the species dimidiata. ZrELLER reports the 
two forms as occuring together. NerRESHEIMER does not say how 
often he saw these peculiar forms, or whether 0. dimidiata was 
present with them. All the Opalinae zelleri I have seen were 
large, all the small individuals present with them, as well as many 
of the large ones, being typical O. dimidiata. The fact that very 
much swollen and stocky individuals of O. caudata are frequent in 
the late winter and in the spring, and the fact that I once found 
a few very thick individuals of O. ranarum, make one suspect that 
the forms called zelleri may be merely similar stocky individuals of 
0. dimidiata. Until this question can be definitely settled, it is — 
convenient, and is apparently justifiable, to give these forms a 
specific name. 
Opalina zelleri (Text Fig. II, p. 206) is the largest Opalina known, 
when we consider its breadth and thickness as well as its length. 
A large example has a length of 0.25 mm anda breadth of 0.13 mm. 
In cross section the animal is circular except that there are present 
upon the body four to eight longitudinal ridges with intervening 
furrows, which show, of course, in cross section. The anterior end or 
the body is bent to one side, as in all other Opalinas. The animal is, 
however, so stocky that the bend is not quite so noticeable as in 
slenderer forms. In O. ranarum the corresponding bend in the body 
is present, but the decided flattening of the body, and its consequent 
great breadth, somewhat obscure the bend. ‘The anterior end of 
