2986 M. M. Metcatr 
clearly an adaptation to copulation and is probably comparable to 
the stickiness of the isogametes in Paramaecium. 
The microgametes usually swim tail foremost, though sometimes 
one finds them swimming in the opposite way. Doubtless the habit 
of swimming with the sticky end of the body foremost is an adap- 
tation to copulation, helping the gametes to become attached. I think 
that the microgametes which an found swimming with the tail 
behind lack the ball of sticky material near the tip of the tail. In 
every case in which this point was noticed it was found to be so, 
but the observations are too few to make one certain that mature 
and immature microgametes can always be distinguished by their 
mode of swimming. The microgametes contain but one nucleus. This 
is usually difficult to see in the living animal, though sometimes it 
shows clearly. No excretory organs or extruded excretory granules 
are seen in the microgametes, but the extruded granules are some- 
times found in the mother-cells from which the microgametes arise 
and in individuals of the preceeding generation. Endosarce spherules 
are present in the microgametes (Fig. 161, 163, Pl. XXIII). Ectosare 
spherules are found in the microgametes of O. caudata (Fig. 259, 
Pl. XXVI) and O. dimidiata, and are doubtless present in the micro- 
gametes of O. intestinalis also, though I find nothing in my notes 
upon this point. 
The gametes arise by longitudinal division in every case which 
I have observed (Figs. 146, 147, 143, XXII, 159, Pl. XXIII). Appa- 
rently transverse division does not occur between the time of hatch- 
ing from the cyst and copulation, though it might be about as 
frequent as in the asexual generation and still very likely not be 
observed. There is nothing of special note in the divisions which 
result in the formation of the macrogametes. Division begins al- 
most always at the anterior end (Fig, 146, 153, Pl. XXII) rarely at 
the posterior end (Figs. 207, 209, Pl. XXIV) sometimes at both ends 
at the same time (Fig. 147, Pl. XXII). The strand of tissue, which 
ultimately is all that is left connecting the two daughters, may lie 
at any level in the posterior two-thirds of the bodies; usually it is 
quite near to the posterior end. 
In the formation of the microgametes the divisions for at least 
two generations do show some divergence from the ordinary di- 
visions. The daughter cells are more slender than usual and they 
seem to have unusual difficulty in pulling apart. The division be- 
gins apparently always at the anterior end of the body and moves 
bockwards until the daughter cells are connected only by the extreme 
