8 9 
Fig. 1. An individual of Opalina antilliensis which has recently come from longi- 
tudinal division i. e. division parallel to the lines of cilia, c-d being the line along 
which the division occurred, and a-b the broad anterior end. 280 diameters. 
Fig. 2. An individual of O. antilliensis, which has just come from transverse division, 
1. e. division transverse to the lines of cilia. The nucleus has not yet completed the 
division by which the binucleated condition is to be reestablished. 280 diameters. 
Fig. 3. An optical section of O. antilliensis, showing that the diameter of each nu- 
cleus is practically the same as the thickness of the whole endoplasm. X 280 diameters. 
Fig. 4. An ordinary full sized individual of O. antélliensis, showing the lines of cilia 
insertion, some of the cilia at the edge in profile, and the two nuclei in outline. X 280 
diameters. 
Fig. 5. Opalina intestinalis, side view and cross section. 
Fig. 6. Opalina caudata, side view and cross section. 
Fig. 7. Opalina dimidiata, side view and cross section. The very numerous nuclei 
are not drawn. 
Fig. 8. O. zelleri, side view and cross section. The very numerous nuclei are omitted. 
Fig. 9. O. ranarum, side view and cross section. The very numerous nuclei are omitted. 
