1910] HOVT—FERTILIZATION IN FERNS 359 
on the slide under a cover glass, and the movements of the sperms 
followed. For other experiments the antheridial prothalli, after 
being rinsed, were placed in a few drops of water; and the sperms, 
after their escape, were transferred to the slide with a pipette. Since 
the sperms are too small to be studied with a binocular microscope, 
most of the observations were made with an ordinary microscope, 
using a Zeiss 8™™ objective. The results given are based on the 
observation of thousands of sperms; they will, of course, not apply 
to every sperm whose movements were followed, but will apply only 
as a kind of average, stating in general the manner of reaction 
observed. ; 
Most of the observations were made on the sperms of Pteris 
multifida, but these results were verified with the sperm of every 
species studied. The structure of the sperms is that of a flat, spirally 
coiled band bearing numerous cilia, especially near their anterior 
ends. Some of them are coiled to the left, others to the right; some 
of them appear to revolve clockwise, others in a counter-clockwise 
direction, and some of them seem at times to change their direc- 
tion of rotation. | 
In water the sperms swim by rapid movements of their cilia, at 
the same time rotating on their axes and swinging their anterior 
ends through small circles. The result of this is that they progress 
in narrow spirals; their course in water approaches a straight line, 
but has occasional turnings. When the sperms are placed in quince 
seed jelly or a solution of India ink, however, their movements are 
strikingly different from those shown in water. They now swing 
their anterior ends through large circles, so that they proceed along 
wide spirals; they no longer pursue a course approaching a straight 
line, but turn here and there again and again. In thick ink they pass 
through spirals larger than those made in thin ink. Fig. 1 shows 
the differences in the spiral courses of sperms in thick ink, in thin ink, 
and in water. When they change the direction of movement, they 
accomplish this by swinging their anterior ends through large circles, 
at the same time revolving on their axes, and then going forward in a 
3 The material of Pieris multifida used in this investigation was obtained from 
Jamaica, B.W.1,, during a visit made by the writer to that island, aided by a grant 
from the Bache Fund. Acknowledgment is here made to the trustees of that fund 
for this assistance. 
