222 M. M. Mercarr 
confident, however, that Contr & Vanry, who worked on O. intestinals, 
refer to certain very evident chromatin spherules in the nucleus, 
which will soon be described. 
Excretory organs 
(Figs. 1,°17, Pl. XIV; 97; Plo XXP;9248——250; Pl XXVD. 
A system of excretory vacuoles is present in the axis of the 
body. I have published a description of these organs (MErcaur 
19076 and c) for the full grown forms of O. intestinalis, O. caudata 
and O. obtrigona and for the small spring individuals and the 
macrogametes (not the microgametes) of O. intestinalis, O. caudata and 
O. dimidiata. Reference must be made to this very primitive excretory 
organ when we discuss the relationships of Opalina, so I include here 
a few figures showing its character, and summarize the chief points 
in the published description. 
In O. intestinalis (Fig. 1) the excretory organ, when highly 
developed, consists of an axial series of more or less irregular fused 
vacuoles, opening to the exterior by a transient aperture at the 
posterior end of the body, and stretching forward usually as far as 
the posterior nucleus, or often nearly to the anterior end of the body. 
In its course, as it passes the posterior nucleus, it lies close against 
the nuclear membrane, usually bending spirally around it. It often 
has a similar relation to the anterior nucleus. Frequently the series 
of fused vacuoles branches behind the posterior nucleus, the branch 
running along another side of the posterior nucleus, which is thus 
almost enveloped by the excretory organ. I have recently found full 
grown O. intestinalis and O. caudata in which the excretory organ 
stretches as far forward as the anterior nucleus. Heretofore I had 
seen the elongated excretory organs only in small forms in the spring. 
Generally the posterior end of the organ in O. intestinalis shows 
one or more enlargements of considerable size surrounded by un- 
usually large granules in their walls (Fig. 97, Pl. XXI, also ef. 
Mercaur 1907b). Usually one sees a mass of such larger granules 
in the cavity of the posterior chamber. These granules stain some- 
what differently from the ordinary endoplasmic granules with most 
stains. They are from time to time extruded from the excretory 
aperture at the posterior end of the body and are cast away. One 
often sees individuals dragging after them a mass of these extruded 
granules (Figs. 248, Pl. XXVI, 147, 153, Pl. XXII). 
