ON THE STRUCTURE OF PROTOPHRYA OVTCOLA: 117 



The pellicula (Fig. 4, pell.) is a dense homogeneous layer and with the exception 

 of the striae above mentioned it shows no structural differentiation. The marginal 

 regions (Fig. 4) bearing the peripheral belt of cilia are much thicker than the dorsal 

 and ventral portions. The pellicula is quite thick and serves, together with the 

 cortical plasma, to give constancy in form to the individual. 



The alveolar layer (Fig. 4, st. ah.) is about a micron in thickness and consists 

 of a single layer of alveoli formed by partitions which are vertical to the pellicula. 

 I have not been able to distinguish any trichocysts in this layer. Mouth and anus 

 are both absent, the only opening in the pellicula being the pore of the contractile 

 vacuole. The myonemes which lie beneath the meridional lines of insertion of the 

 cilia are feebly developed in keeping with the slight flexibility of the body. 



The entoplasm (Fig. 1, en'pl.) in living, preserved, and stained material is less 

 dense than the cortical plasma, and in both iron hematoxylin and picrocarmine 

 it stains more deeply. It contains many larger granules (Figs. 1, 4), and its substance 

 is much more fluid than that of the outer layer. Some of the granules are more highly 

 refractive than others, and in staining these granules dye more deeply. There is 

 usually a larger one, 6 to 8 micra in diameter, near the anterior end which at first 

 glance suggests a micronucleus, but its consistency, its inconstancy in different indi- 

 viduals, and the presence of granules which intergrade between it and the less deeply 

 stained ones preclude such a possibility. It seems to be a highly differentiated meta- 

 plasmic constituent. 



The cortical plasma (Fig. 4, pi. ctx.) occupies a marginal belt (in dorsal or ven- 

 tral view) about 8 to 12 micra in width and a much thinner stratum on the dorsal and 

 ventral faces. In living animals it is hyaline and homogeneous. In preserved 

 material it has the appearance of an alveolar structure with denser granules of 

 minute and somewhat variable size scattered throughout its substance Its inner 

 margin is somewhat irregular with short centrally directed angles (Fig. 1), and it is 

 marked by an abrupt change to the more coarsely granular and more mobile 

 entoplasm. 



The contractile vacuole (Figs. 1, vac. co'tr., 2, 6, 7) lies at the posterior end in 

 the cortical layer of the ectoplasm. At diastole it is 12 to 15 micra in diameter and 

 of spherical form or slightly flattened in dorso-ventral direction. A trefoil-shape 

 (Fig. 7) was found in one instance in preserved material and may indicate the 

 approach of systole. Even at the time of diastole the outer layer of entoplasm 

 forms a distinct membrane of denser cytoplasm which separates the vacuole from 

 the looser entoplasm of the central region with the exception of a small area at the 

 anterior pole where only the wall of the vacuole intervenes (Figs. 6, 7). 



