Opalina. 361 
slightly rolled. These are all distinct. A few dissolving chromatin spherules are 
shown near the constricted end of each daughter nucleus. The nucleolus is not 
drawn.. Coros. subl.-acetic acid, DeLarrenpy’s haematoxylin. > 1600 diameters. 
Fig. 66. Outlines of the nuclei and anterior end of the body of another 
individual. X< 404 diameters. 
Fig. 67. The posterior of the two nuclei shown in Fig. 66. Only the granular 
chromatin ribbon and a little of the achromatic foam is shown. Coros. subl.-acetic 
acid, DELAFIELD’s haematoxylin. > 14600 diameters. 
Fig. 68. The anterior end of a binucleated individual, showing in each nucleus 
the chromatin ribbon beginning to break up into the chromosomes preparatory to 
the next mitosis. The achromatic granules are conventionally drawn. The nucleolus 
is not shown. Coros. subl.-acetic acid, DreLarreip’s haematoxylin. >< 808 diameters. 
Fig. 69. A thin optical section through the posterior nucleus shown in 
Fig. 68. All the granules in the chromosomes and the achromatic granules and 
film-lines are accurately drawn, except that the level of some of the achromatic 
granules is not correctly shown. X< 1600 diameters. 
Fig. 70. The anterior end of an individual in whose nuclei the chromatin 
ribbon has apparently already constricted to form separate chromatin masses, 
although, from the short thread connecting them, the nuclei seem to be young. 
The chromatin masses of only the upper half of the nuclei are drawn. The spheri- 
cal nucleolus is seen in the posterior nucleus. Coros. subl.-acetic acid, DELAFIELD’s 
haematoxylin. > 808 diameters. 
Fig. 71. The anterior end of an individual with two nuclei. The chromatin 
masses of only the upper half of the nuclei are drawn. The spherical nucleolus 
is seen in the posterior nucleus. Chromatin spherules are forming from the chro- 
matin masses. Coros. subl.-acetic acid, DeLarieLp’s haematoxylin. >< 808 diameters. 
Fig. 72. The anterior end of an individual with two nuclei in which the 
chromatin spherules are for the most part already separated from the chromatin 
masses. The old nucleolus is seen in the posterior nucleus. A new nucleolus is 
forming near the pointed end of the anterior nucleus. Coros. subl.-acetic acid, 
Derarretp’s haematoxylin. >< 808 diameters. 
Fig. 73. The old nucleolus and a single chromatin mass from a nucleus in 
a condition slightly earlier than that shown in Fig. 72. The chromatin mass is 
granular, as the chromosomes always are. The chromatin spherules, much larger 
than the chromatin granules, are about to be cast off. Coros. subl.-acetic acid, 
Derartetp’s haematoxylin. >< 1600 diameters. 
Fig. 74. An injured daughter cell (posterior end broken) whose nucleus shows 
the only exception I have found to the rule that in this species the old nucleolus 
remains in the posterior daughter nucleus. In this case it is in the anterior daughter 
nucleus. No attempt is made in this small scale drawing to represent all the 
chromosomes. Coros. sub].-acetic acid, DeLariripd’s haematoxylin. > 368 diameters. 
Plate XX. 
Opalina intestinalis and O. caudata. 
All figures are reduced one-fifth, to the magnification indicated. 
Figs. 75—80. Opalina intestinalis. 
Fig. 75. The posterior nucleus of a binucleated individual, entering upon 
mitosis. Numerous faintly stained partially dissolved chromatin spherules are 
