342 M. M. Mercaur 
describes (p. 62) the drops of liquid which exude from the ectosare 
of Opalina when pressed; the fact that they do not mix with the 
water; and the further fact that on relieving the animal from 
pressure the drops are again absorbed by the body. These he 
regards as drops of hyaloplasma. ScuHNnermeEr says (p. 71) that 
the protoplasmic currents, so general in the Jnfusoria, are entirely 
wanting in Opalina. His discussion of the hyalo plasma (p. 83—111) 
is based in part upon his studies of Opalina. He strongly opposes 
Birscuui’s belief in the prevalence of alveolar structure in living 
protoplasm. [It seems to me that few objects could be found more 
satisfactory than O. itestinalis and O. caudata for demonstrating 
the alveolar structure of protoplasm. | 
JENNINGS (1906) describes the “avoiding reaction” in O. ranarum, 
and its behaviour with reference to acid and alkaline media showing 
that Opalina’s reactions to stimuli, like those of other Protozoa, are 
always negative or null, never positive; he also quotes, with figures, 
WALLENGREN’S analysis of the reaction of the cilia of this species 
to electric stimuli of different intensities. 
NERESHEIMER (1906 preliminary notice, and 1907) is the first 
to recognise the presence of gametes in Opalina and is the first to 
describe the extrusion from the nuclei of the chromatin spheres 
previously described as micronuclei by LOEwENTHAL. He saw no 
splitting of the chromosomes, confirming TONNIGES and BEZZENBERGER 
against Prirzner. He found the chromosomes in the asexual forms 
of O. ranarum and O. dimidiata to be apparently 12 in number. 
He describes in detail phenomena preceeding encystment in the 
rectum of the frog; the process of encystment and the character of 
the infection cysts; the hatching of the cysts in the rectum of the 
tadpole; the formation of isogametes and their copulation; encystment 
following copulation; a spindle-like shape of the male and female 
pronuclei in the copulation cysts, and of the large syncaria of the 
zygotes. He gives the name QO. zelleri to the large stocky form 
which Zetuer found with O. dimidiata in Rana esculenta, having 
himself seen the same form in the same host. On the basis of its 
manner of reproduction, he regards Opalina as related to the Plasmo- 
droma rather than to the Ciliophora. [In many points the results 
of my study are opposed to NeREsHEIMER. Some of his statements 
and beliefs to which I am unable to subscribe are: — his detailed 
description of the formation of generative chromidia, the degenera- 
tion of the old nuclei, and the formation of new sexual nuclei from 
the generative chromidia and refractive spherules, all of which is 
