II. The Cytology of the Gametophyte Generation. 19 1 
the reaction is partial it generally appears in the central antheridia only, an 
additional confirmation of the greater vigour of this region. 
Much time and trouble have been expended in trying to find whether 
there is a second cilium or not. In the Fucaceae, as is well known, the 
posterior cilium is very long but very much thinner than the anterior one. 
The possibility had to be considered that in Dictyota the second cilium 
is so reduced in length as to be quite rudimentary, or that it is attenuated 
to such an extent as to be indistinguishable. In the upper left-hand corner 
of Fig. 17 is represented an apparently biciliate antherozoid, and several 
more such cases have been observed. After a careful comparison with 
fixed and stained antherozoids of the Fucaceae I have failed to satisfy 
myself that these appearances are not due to strands of mucilage. In the 
living condition I have only once seen anything suggestive of a second 
cilium. On one occasion, while examining a number of antherozoids by 
means of Zeiss’s D* water-immersion objective, one was observed which had 
got stuck fast at the bottom of the dish. In almost all cases of the kind it 
is the end of the long cilium that becomes attached ; in this instance, 
however, the cilium was quite free, and it could be clearly seen violently 
lashing about in the water. Careful observation showed that the antherozoid 
was attached to the glass by a filament of much greater tenuity than the 
cilium, and of about the same length as the body of the sperm. This 
is the strongest evidence yet obtained for a second cilium, but even 
this is quite insufficient to enable one to come to a positive decision on 
the point. 
III. The Fertilization of the Egg. 
Thuret, Re'inke*, and other investigators tried to solve the question 
of the mode of fertilization in Dictyota. Their failure to obtain active 
antherozoids for their experiments prevented them from arriving at a correct 
solution of the problem. It was further complicated by the fact that many 
of the eggs segmented in the total absence of antherozoids. Among the 
various suggestions advanced from time to time in explanation of the 
difficulty were the following : — 
(1) That fertilization is effected before the liberation of the eggs from 
the oogonia ; this seemed to explain the apparent germination of liberated 
oospheres in the absence of sperms. 
(2) That there are two kinds of asexual spores. 
(3) That the antherozoids have become functionless and that the eggs 
are habitually parthenogenetic. To Johnson, in his study of Dictyopteris , 
belongs the credit of having first pointed out the true answer to the 
question, though his somewhat tentative pronouncements were never con- 
firmed by him. 
The present investigation has now conclusively demonstrated that 
