Opalina. 305 
habit does not argue against its primitive nature. The secluded 
habitat of parasitic life, like that of deep sea life, has enabled many 
species to retain lowly character without extermination. The question 
of the primitive or secondary character of Opalina must be studied 
therefore chiefly through an examination of the structure of the 
animal itself in comparison with other forms. 
In its cilia Opalina in as highly developed as most holotrichous 
Ciliata. The absence of a gullet seems probably secondary, an 
adaptation to parasitism, since it uses predigested dialyzable food 
from the rectum of its host and has no need of ingesting solid food. 
Even Mastigophora, which are doubtless more primitive than Opalina, 
have a gullet which is functionally comparable with that of Ciliata. 
Those species of parasitic Ciliata which retain the mouth have prob- 
ably adopted the parasitic habit more recently than Opalina. 
Chromidina elegans, which in certain conditions of its nuclei resembles 
the multinucleated Opalinae, has what has been interpreted as a 
vestigial mouth GonpEeR (1905). So also has <Anoplophrya brasili 
(L&crr & Dusosca 19046). Lana (1901) classes Opalina with the 
Hymenostomidae among the Ciliata holotricha, describing the suborder 
Hymenostomidae as possessing an undulating membrane and as having 
the mouth always open. Of course Opalina has neither undulating 
membrane nor mouth, yet Lana’s phrase, “mouth always open”, 
suggests a very interesting interpretation, which, however, he doubt- 
less did not intend, namely, that the mouth (ingestion tube) of 
Opalina has disappeared by becoming shallower until finally it has 
joined the even contour of the outer surface of the body, being no 
longer distinguishable from the latter. This seems not at all un- 
likely in view of GonprEr’s description of the mouth of Chromidina 
as a shallow pit over whose walls run rows of cilia continuous 
with and similar to those on the surface of the body, and also in 
view of Licrer & Dusoscq’s description of a vestigial mouth in 
Anoplophrya brasili. 
The presence of functional vegetative and reproductive chro- 
matin in the same nucleus in Opalina seems surely more primitive 
than their segregation in separate nuclei in higher Czlata. In 
Opalina, spherules of vegetative chromatin are formed in the nucleus, 
are then dissolved and pass into the cytoplasm, where very likely 
they take part in forming the refractive spherules. In Hoplitophrya 
the functional vegetative chromatin is in a macronucleus distinct 
from the micronucleus. In this macronucleus refractive spherules 
are formed. (This process has not yet been described, Text Fig. VIII, 
