118 ON THE STRUCTURE OP PROTOPHRYA OVICOLA. 



Leading from the vacuole through the cortical plasma is an efferent canal (Figs. 

 1, 2, can. eff.) which opens at a short distance dorsal to the posterior margin by an 

 excretory pore (Figs. 1, 2, 6, 7). The pore and canal are not always placed in the 

 median plane, being frequently displaced a little to the right (Fig. 1), possibly as a 

 result of the state of contraction of the animal. This canal and pore are well defined 

 and can be located in all the individuals that I have examined. The pore lies at 

 the summit of a small elevation that sometimes protrudes beyond the posterior mar- 

 gin. The proximal end of the canal connects with the postero-ventral region of the 

 vacuole (Fig. 2). The cytoplasm of the cortical region adjacent to the canal and 

 vesicle stains more deeply and appears to be denser, as though there were a differen- 

 tiated wall to these regions. This wall also' covers the portion of the vacuole which 

 at diastole projects into the entoplasmic region. 



Protophrya is the only member of the family Opalinidse which possesses a single 

 spherical vacuole. In Anoplophrya there are five to thirty, in Hoplitophrya there 

 are two or more, or a longitudinal canal, in Discophrya there is a secreting canal, 

 while in Opalinopsis and Opalina there are no vacuoles at all. Protophrya is thus 

 the least modified member of the family, resembling the non-parasitic and unmodi- 

 fied Holotricha in this particular. 



The macronucleus (Fig. 1, mak'nl.) is centrally located, spherical or slightly 

 flattened in a dorso- ventral direction. It is somewhat variable in contour, being sub- 

 ject to very slight irregularities (Fig. 7). These are never sufficient, so far as I have 

 observed, to give it an elliptical or reniform outline. The diameter in the frontal 

 plane is 20 to 25 micra. Within the nuclear membrane one finds in stained material 

 very many fine chromatin granules or rods evenly distributed throughout the nucleo- 

 plasm. In individuals subjected to the action of 5% sodic carbonate and subse- 

 quently stained in picrocarmine (Fig. 5) I find larger granules that grade down to 

 the smaller ones, each surrounded by a clear area. The larger granules were occa- 

 sionally seen in other nuclei not so treated, but the clear areas surrounding them 

 were not observed. It seems probable that they are due to the solvent action of 

 the reagents. In no other genus of this family is there a single spherical macronu- 

 cleus similar to that found in Protophrya and most Holotricha. The form in other 

 Opalinidse is elliptical as in Hoplitophrya and Discophrya, or even much elongated 

 as in Anoplophrya, while in Opalinopsis and Opalina there are many small elliptical 

 or spherical nuclei. 



The micronucleus (Fig. 1, 5, mik'nl.) is a small elliptical body on the anterior 

 face of the macronucleus. It is from 3 to 5 micra in length with the long diameter 

 in the transverse direction. In stained specimens it can be detected by its deeper 



