COPULATION OF GAMETES.—ECTOCARPUS. 65 
COPULATION OF GAMETES. 
The gametes of Ulothrix zonata are rounded or oval cells, bearing 
two cilia at the anterior end (Fig. 17, E), Each contains a nucleus, 
a red eye-spot, situated about midway between the ends of the cell 
near the surface, and a chromatophore. According to Strasburger 
the cilia are developed under the influence of the nucleus and from the 
anterior, colorless portion or mouth-piece, which consists mostly of 
kinoplasm. In his later investigation of the subject of swarm cells, 
Strasburger (1900) finds that the cilia arise from a local kinéplasmic 
thickening of the plasma membrane at the anterior end. As already 
mentioned in a preceding paragraph (p. 47), he regards this thicken- 
ing as the homolog of the blepharoplast of the Archegoniates. In the 
swarm-spores of H/ydrodictyon, Timberlake finds a small body at the 
base of the cilia, which, in some cases at least, was not a part of the 
plasma membrane. 
The gametes copulate in pairs immediately after they escape from 
the gametangium (Fig. 17, F, G). It is probable that they may be 
brought together, or at least held together after coming in contact, by 
means of a chemotactic stimulus. The stigmatic or eye-spots do not 
unite, but remain separate and independent in the young zygote (Fig. 
17, H). There is no doubt of a nuclear fusion, but how soon this 
takes place after conjugation is not known, so far as the author is aware. 
In Hydrodictyon the gametes are small, oval in shape, biciliate, 
containing one nucleus and, according to Klebs, two pulsating vacuoles. 
They conjugate in pairs immediately on escaping from the gametan- 
gium, but I have observed that conjugation may sometimes take place 
within the mother-cell. If, however, copulation does not follow soon 
after the gametes are set free, they become incapable of uniting, come 
to rest and disorganize. Whether ‘this is a rule was not determined. 
ECTOCARPUS. 
Among the isogamous Phaeophycee the sexual process is doubtless 
best known in Ectocarpus siliculosus Lyngb. from the investigations 
of Berthold (’81), which have been confirmed and extended by Oltmanns 
(’99). ctocarpus is of especial interest in this respect, since it repre- 
sents a transition from isogamy to heterogamy. In fact, there is in the 
brown algz, as well as in phylogenetic series of other Thallophyta, 
every transition from the type of gametes found in Hctocarpus to that 
of Fucus, The gametes, although nearly or quite the same size and 
appearing morphologically alike, are physiologically different, and we 
may, with much propriety, speak of egg-cells and spermatozoids. 
