400 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
karyokinetic process similar to that seen in the preceding divisions. Of 
the two resulting nuclei in each cell, one is a “ wandering nucleus ” and 
migrates into the other individual ; the fate of the other is not certain, 
but it is believed to disappear ; there was no evidence of a fusion of 
wandering and stationary nuclei, as in Paramoecium according to Maupas. 
After the migration of the wandering nuclei, these undergo marked 
change of form, becoming greatly elongated, and form a spindle which is 
nearly as long as the body. The two nuclei formed in this way lie at 
the posterior ends of the bodies of the individuals. Each again divides, 
and with the formation of these four, nuclear conjugation is at an end 
and the individuals separate. During its course the macronuclei have 
degenerated, and a new macronucleus in each individual is formed by 
the union of two of its four nicronuclei. The remaining two nuclei 
form the micronuclei of the two new individuals formed by division, 
while their macronuclei are formed by the division of the single macro- 
nucleus. 
In a discussion of the theoretical bearing of his results, the author 
rejects the attempts which have been made to closely homologise the 
cell-organs and processes of cell-division in the Ciliata with those of 
the Metazoa, and states his belief that the Ciliata were a very early off- 
shoot from the Protozoan stem. In the first divisions of the micronuclei 
of conjugating Ciliata he recognises clear homologies with the reducing 
divisions of the Metazoan egg, but he does not believe that anything 
corresponding to a union of sexual nuclei occurs in the Ciliata. In other 
words, he doubts the occurrence of the fusion of wandering and stationary 
nuclei in conjugating Ciliata as described by Maupas and Hertwig. He 
believes that the essence of the process is the introduction of a new nucleus 
and new cytoplasm into the exhausted individual. 
Protozoan Nuclei.* — Mr. G. N. Calkins maintains that Metazoan 
and Protozoan nuclei qannot be strictly homologised, but it can be shown 
that an intermediate series of forms connect them. The nuclei of Proto- 
zoa are not all of the same type, and in some forms they may possibly 
be absent. The simplest structure is the distributed nucleus, consisting 
of isolated chromatin granules scattered about the cell. A higher type 
is shown by the “ intermediate ” nuclei, where the chromatin granules are 
massed together in a compact form with or without a nuclear membrane 
(most Euflagellates). Typical nuclei of the Metazoan type are uncommon 
among the Protozoa, but are occasionally found. 
Nuclear differentiation in Protozoa is closely connected with an 
attraction-sphere or active agent in division. In nuclei of the distributed 
type this is an indefinite faintly staining cytoplasmic mass, in the vicinity 
of which the scattered chromatin granules collect previous to division, 
and about which they are grouped during division. In nuclei of the 
“ intermediate” type the attraction-sphere is intranuclear, definite in form, 
deeply staining, and active, and chromatin granules are massed about it 
either permanently ( Synura , Chilomonas, Euglenoids, &c.), or only during 
division ( Paramceba ), and with or without a nuclear membrane. In 
higher types of nuclei the attraction-sphere is no longer intranuclear, 
but this position of vantage is taken by the central spindle during 
* Ann. New York Acad. Sci., xi. (1898) pp. 379-97 (1 pi.). 
