224 M. M. Meroatr 
system of irregular, branching canals is more developed than the 
excretory organ of Opalina in having 1) a definite limiting membrane, 
2) a permanent external aperture, and 3) cilia lining the outer 
portion of its duct, and also in being evidently a permanent organ 
of the cell. 
In my first paper on the excretory organs of Opalina (Mrrcar, 
19076) 1 wrote: “Under pressure from a cover-glass, in gradually 
drying preparations, oil globules are generally protruded from the 
body at different points on the periphery. The largest of these oil 
globules is generally found at the posterior end of the body” [in 
connection with the excretory pore] “and is usually the first to 
appear, in spite of the fact that the posterior end of the body is 
the most slender part and must be the last to feel the pressure.” 
Further observation shows that I was mistaken in describing any 
special connection between the excretory pore and an especially 
large drop of this exuded liquid. Often a drop is found here and 
it. may be large, but observation of a much larger number of Opalinae 
under pressure shows that it was an error to emphasize the size 
and early appearance of this drop. The exuded liquid is not oil, 
but is either the protoplasm itself, or is derived from the protoplasm. 
It cannot be derived from the ectosarc spherules, for similar exuded 
drops are found in Ciliata which have no ectosare spherules (cf. also 
Kouscu 1902). 
Nucleus, and mitosis. 
Few if any known nuclei among the protozoa are clearer and 
better for study than those of O. itestinalis and O. caudata; the 
nuclei are large and the chromatin is small in amount and does not 
obscure the achromatic structures; the chromosomes are few in 
number, eight in O. intestinalis and six in O. caudata; all the structures 
usually found in typical nuclei, including a plasmosome nucleolus, 
are present and stain readily and distinctively; and, as already 
mentioned, all the structurec in the nucleus are sometimes very 
clearly seen in the living animal. I have therefore given chief 
attention to the nuclear phenomena, especially those of mitosis. 
Opalina intestinalis has usually two ovoid nuclei lying in the 
anterior half of the body, sometimes in the anterior third (Fig. 1 
and Pl. XVII, Fig. 38). The ends of the nuclei which are turned 
towards each other are generally more or less pointed. Commonly 
these pointed ends are connected by a more or less elongated delicate 
strand consisting of the attenuated nuclear membrane, which was 
