Opalina. 289 
but one more division to form definitive microgametes) was twenty- 
two. Similar proportions, but with smaller numbers, were frequent. 
Copulation. 
In copulation a microgamete fuses completely with a macro- 
gamete (Figs. 210—217, Pl. XXV, also 164—182, Pl. XXIII). The 
first contact is purely accidental, there being no evidence of any 
attraction of the gametes for one another. NerresHrmmer describes 
the short-straight-tailed forms in O. dimadiata, which he interpreted 
as gametes, as circling around each other, as if under the influence 
of some mutual attraction. May this not have been merely the usual 
spiral movement seen in all Ciliata and Flagellata, appearing circular 
in this case because confined by the slide and cover-glass almost 
to one plane? The microgametes cling to anything which they touch 
with their sticky tails, though they seem never to cling to one 
another. Indeed I believe I have never happened to see two of 
them in contact even for a moment. 
The animals in the rectum gather chiefly in a single group 
(sections of the recta show this clearly). They have the same 
habit of gathering in groups in the slide cultures, collecting usually 
about some bit of foecal matter. In such a group there are often 
thirty to one hundred forms which look like macrogametes and per- 
haps a dozen microgametes. The latter are constantly striking the 
macrogametes, clinging to their cilia and again breaking away, 
either because of the active swimming movements of the macro- 
gametes, or because of violent contact with other individuals. Even 
true copulating pairs may be torn apart by other individuals 
swimming between them. In two such instances copulation between 
the intruder and the microgamete immediately followed. Frequently 
two (O. caudata, Fig. 271, Pl. XX VII) and once three microgametes 
were seen attached to the cilia of one macrogamete. Microgametes 
were seen attached to individuals in an advanced stage of division 
to form two macrogametes (O. caudata, Figs. 269, 270, Pl. XX VII). 
They seem readily to attach to any of the individuals of the macro- 
gamete type. 
The loose attachment of the microgamete to the cilia of the 
macrogamete changes to the closer union and ultimate fusion of co- 
pulation (Figs. 210—217, Pl. XXV, various, stages on Pl. XXIII, 
cf. O. caudata, Pl. XXVII). The tail of the male fuses at its tip 
with the body of the female: then the tail of the male becomes 
