Opalina. 313 
Keuten 1895, Euglena viridis; Cauxtys 1901, Clepsidrina; HARTMANN 
& vy. Prowazex 1907, numerous Plasmodroma.) 
These are not functional mitotic spindles in these degenerating 
nuclei of QO. obtrigona. The nuclei, though they become elliptical, 
do not divide, but soon go to pieces, leaving spaces in the cytoplasm 
where they lay (Fig. 118). During the process of degeneration the 
nuclear membrane becomes fainter and fainter and ultimately entirely 
disappears. Sometime the chromatin sphere, including both the 
chromatin net and the central refractive body, is extruded into the 
cytoplasm, leaving within the degenerating nucleus only one or 
more masses of debris representing the achromatic structures (Figs. 
116 and 117). In other cases one finds the degenerate chromatin 
sphere lying in the space from which the nucleus has dissappeared. 
The chromatin sphere itself resembles those of the cysts (cf. 
Fig. 133, Pl. XXII), and its extrusion is propably comparable to that 
of the latter. That is, under unfavorable conditions, the degene- 
rating nuclei undertake a part of the activities which usually 
preceede copulation. I have not found a perfectly clear spindle-like 
arrangement of the achromatic granules in the nuclei of the cysts 
or of the minute individuals in the spring which were preparing 
to extrude the vegetative chromatin, but most of my material of 
these forms was stained with acetic-carmine which does not give 
sharp pictures of the finest details. In sections of cysts stained 
with Drtarienp’s haematoxylin, one sees in the center of the nuclei 
groups of granules (Figs. 134, 136—139, Pl. XXII) resembling those 
in the earlier stages of degeneration in the nuclei of O. obtrigona 
(Figs. 105—109, Pl. XX1). Up to this point the two sets of phe- 
nomena, normal and abnormal, seem quite comparable. The granular 
spindles and polar masses do not seem to be paralleled in the 
normal nuclei at any stage of the life cycle. Their resemblance, 
however, to what is found normally in some Plasmodroma, e. g. 
Amoeba cristalligera, is such as to suggest that these abnormal phe- 
nomena in degenerating nuclei of O. obtrigona are a reminiscence of 
archaic normal conditions. 
The abnormal phenomena described in this chapter are probably 
due to unfavorable conditions of life. Their resemblance to some of 
the phenomena usually preceeding copulation suggests comparison 
with the well-known fact that many animals, e. g. Rotifera, Cladocera, 
which reproduce asexually under favorable conditions, are induced 
by unfavorable conditions to introduce sexual phenomena. 
