260 M. M. Mercatr 
acteristic of the higher Ciliata. Opalina shows, therefore, a condition 
intermediate between that of Flagellata and that of the higher (i- 
liata, since, while retaining the more primitive type of division, it 
shows occasional divisions of the secondary type. The flattened 
multinucleated species of Opalina show more frequent transverse di- 
visions than do the probably more primitive cylindrical binucleated 
species. 
The phylogenetic significance of these phenomena is further 
considered on page 274 in connection with the discussion of the 
relationshipes of Opalina and the origin of distinct micro- and macro- 
nuclei in higher Cvliata. 
Time relations in the division of the body and of the nucleus. 
The two sets of daughter chromosomes in each nucleus of the 
binucleated Opalinae remain for one cell-generation in the same 
daughter cell, though soon separating into different nuclei; that is, 
division of the body lags one step behind the division of the nuclei. 
At the second division of the body the daughter chromosomes of the 
preceeding division become distributed to separate cells. Probably 
originally the binucleated condition was brought about by the de- 
lay of one division of the body, the temporary binucleated con- 
dition thus secured persisting until the body itself finally divides. ') 
The multinucleated condition of other species seems due to the 
further suppression of other divisions of the body, nuclear division 
and division of the body in them being still more loosely related. 
Splitting of the chromosomes. 
In the mitosis of Opalina we do not find any longitudinal split- 
ting of the chromosomes in connection with the imperfect equatorial 
plate stage. The chromosomes are then already present in nearly 
or fully the double number and, while one or two chromatin masses 
may constrict transversely during the equatorial plate stage, the 
majority merely rearrange themselves in two transverse rows pre- 
paratory to migration to the poles. Careful observation of the chro- 
mosomes in both ends of many nuclei during the anaphases shows 
that generally each chromosome in one end of the nucleus corre- 
1) I find that Boverr (1900, p. 189) has similarly interpreted the binucleated 
condition of Opalina as due to delay in the division of the cell-body. 
