66 FECUNDATION} MOTILE ISOGAMETES. 
Both Oltmanns and Berthold agree in the opinion that Hetocarpus 
stlicudosus may be either moneecious or dicecious, for they observed 
individuals whose gametes would not conjugate with each other, but 
only with those of another individual. As is well known, the gametes 
are generally borne in the so-called plurilocular sporangia. The details 
in the process of nuclear and cell-division in the development of both 
gametes and asexual swarm-spores have not, as yet, been thoroughly 
studied. The gametes (Fig. 19, A) are pear-shaped cells with a chro- 
matophore, nucleus, a reddish brown eye-spot, and two cilia inserted 
laterally. The cilia are of unequal length, the longer extending for- 
ward and the shorter backward. 
The conjugation of the gametes can be most readily followed in a 
hanging drop, into which both male and female gametes are intro- 
duced, when the whole process may be observed with the aid of the 
highest magnifying powers. The female gametes, as a rule, first come 
to rest, and about each one numerous spermatozoids assemble. If the 
female gamete comes to rest at the edge of the drop, the male cells 
cluster about it, attaching themselves apparently by the anterior cilium, 
giving the familiar picture figured by Berthold (Fig. 19, A). But 
should the female gamete attach itself to some particle hanging in the 
arched surface of the drop, this cell then appears as a circular disk 
surrounded by a wreath of male cells radially disposed. Shortly a 
male gamete (in exceptional cases two), having attached itself to the 
female by means of the anterior cilium, approaches the latter appar- 
ently by the sudden contraction of the same and unites with it, while 
the remaining male gametes withdraw (Fig. 19, B, C). In a few 
minutes cytoplasmic union is complete, and within about ten hours 
after copulation both nuclei have fused (Fig. 19, E, F, G). The 
chloroplasts do not unite, a fact which is contrary to the peculiar 
phenomenon described by Overton for Spzrogyra (see page 69). 
The sexual process in Ulothrix, Hydrodictyon, and Ectocarpus 
may be considered as fairly typical of the lower alge in which fecun- 
dation consists in the fusion of motile isogametes. In this, probably 
the simplest and most primitive sexual process, as in the higher plants, 
it will be seen that fecundation consists in the fusion of the sexual 
nuclei together with the cytoplasm of the gametes, but the fusion of 
the nuclei must be regarded as of prime importance. 
