324 M. M. Mercarr 
vigorous movements arise, followed by protrusions from the body as 
if it were broken, and finally the body became completely flat. 
“With moderate currents, at the first stimulation the animals drew 
back strongly, then lay entirely quiet in a sort of tetanus of all 
the muscles, if they were not carried forward by the action of the 
cilia, upon which the current seemed to have absolutely no influence.” 
If the stimulus was strengthened, constrictions soon appeared and 
then breaks at different places at the edge of the body. In this 
condition many animals swam about for a considerable time if the 
stimulus was removed. After long stimulation with very strong 
currents the whole animal liquefied, forming a shapless flat mass 
(“unférmigen Brev”) in which for a long time the cilia here and 
there would continue moving. 
Stem (1859) mentions (p. 72) Opalina as belonging to the 
holotrichous Infusoria; he again refers (p. 75) to the divergence of 
this genus from the rest of the Jnfusoria in its lack of mouth and 
anus and in absorbing liquid food through the surface of the body; 
he describes (p. 91) the presence of many vacuoles with definite 
contour, filled with liquid containing granules. [This reference is 
apparently to the nuclei.| Division or budding had not up to that 
time been observed in O. ranarum (p. 94). He says he had sought 
in vain for a nucleus in O. ranarum (p. 94). 
Sremn (1860, p. 54) again emphasises the divergence of the 
Opalinas from the other holotrichous Jnfusoria. He says the former 
genus Opalina divides itself into several genera: Discophrya includ- 
ing the forms with a sucking disc at the anterior end of the body; 
Hoplitophrya including the forms bearing horny hooks at the anterior 
end of the body; Anoplophrya including forms, nearly related to 
Hoplitophrya but without discs or hooks, which have simple nuclei 
in the axis of the body and contractile vacuoles of different forms; 
and Opalina including O. ranarum, the form longest known, and 
O. dimidiata,’) a nearly related, slenderer, more elongated form, 
also living in the alimentary canal of the frog. These two species 
have no contractile vacuoles and no ordinary nuclei, but instead 
have numerous small nucleus-like structures scattered through the 
whole parenchyma. 
PrircHarp (1861) describes at considerable length the Opalinidae, 
giving however but little attention to O. ranarum the only true 
Opalina he recognises. He says of O. ranarum that the mouth 
1) T have not found Srer’s original description of O. dimidiata. 
