540 
lina. In the accompanying paper, “Chromosomes in Opalina”, some of 
the features of its nuclear structure are figured and described. A brief 
description of its diagnostic characters, with figures, is here given. 
Opalina antilliensis is a binucleated, much flattened species resem- 
bling the less flattened O. macronucleata Bezzenberger, and very 
closely resembling O. binucleata Raff. Raff figures the lines of cilia 
as longitudinal in her species, instead of oblique, or more properly spi- 
ral, as in all other species. The nuclei as figured by Raff are much 
smaller than in O. antilliensis, but Raff's statement of the dimensions 
agrees with what I find in O. antilliensis. If the stated dimensions, 
rather than those figured, in Raff’s paper are correct, and if the lines 
of cilia were spiral instead of longitudinal as figured, the agreement with 
O. antilliensis would be exact. But, of course, Raff’s description must 
be taken as it stands. Even if there were no observable differences in 
structure between the two species, one from Bufo agua in Jamaica, the 
other from Limnodynastes dorsalis and L. tasmaniensis from Australia, 
my study of the genus as a whole and of its tendency to most comple- 
tely intergrading speciation would lead me to doubt the consanguinity 
of these two forms. I think even practical identity of structure would 
not be a sufficient indication of consanguinity in forms of such diverse 
and widely separated habitats. This question, however, must be reser- 
ved for discussion in a more comprehensive study of the taxonomy in 
this genus. . 
In form Opalina antilliensis varies between the limits shown in the 
accompanying figures. Individuals that have recently come from longi- 
tudinal division, i. e. division parallel to the lines of cilia?, may be 
broadly triangular (fig. 1). Individuals recently come from transverse 
division, i. e. division transverse to the lines of cilia, may be much more 
slender (fig. 2). The usual shape is in general broadly oval (fig. 4), but 
one familiar with the form of other species of Opalina recognises several 
features whose significance is best brought out by comparison. 
In all the Opalinas, the anterior end of the body is bent to one side. 
In the cylindrical forms, whether binucleate like O. intestinalis (fig. 5), 
or multinucleate like O. dimidiata (fig. 7), this is very evident. In the 
flattened forms this bending of the anterior end to one side is obscured 
by the flattening and by the fact that the anterior end is usually very 
broad (fig. 9). In figure 8 the anterior end is the portion between a and 
b. It is demarcated from the rest of the body, on one side, by a more or 
less evident indentation c. The posterior end is shown at d. The lines 
of cilia are slightly oblique, i. e. spiral, as in all holotrichous Ciliata. 
2 Usually called oblique division. 
