MOVEMENT OF SPERMATOZOIDS. 59 
spermatozoids being soft and very elastic, recover their shape after the pressure is 
past. The spermatozoids are next shown in figure 3 in the process of getting out of the 
mother cell, after which they swim freely in the pollen tube, from which they gen- 
erally escape later. In general, there are two modes by which they get out of the 
pollen tube, viz, (a) gradually, (b) suddenly, and this difference depends chiefly on 
the density of the surrounding fluid. (a) Mode of gradually escaping: Figure 4 shows 
an example of a spermatozoid gradually getting out of the tube, observed in Tokyo. 
At 4.15 p. m. (September 17) the head of the spermatozoid made its appearance a 
little out of the pollen tube and after five minutes it entirely got out of the tube and 
recovered its normal shape. Then it swam with a definite rate until 5.45 p.m. From 
this observation it can be seen how soft and elastic the body is. This is very similar 
to the escape of the swarm spores of (2yodonium or the spermatozoids from its old 
cell wall, because also in this case the shape of the swarm spore or of the spermato- 
zoid, before and after getting out of the old cell wall, are quite different, like that of 
the spermatozoid of Ginkgo. They also have an oval shape with numerous cilia. 
(b) Mode of suddenly escaping: In this case the membrane of the mother cell con- 
taining the two spermatozoids (also with Hirase’s two cytoplasmic cylinders?) is sud- 
denly thrust out of the pollen tube, as shown in figure 5 xxx. At first the shape of 
the spermatozoid is very irregular because of the surrounding pressure produced by 
-sudden protrusion, but gradually it separates from the mother cell and takes the form 
shown in } and 0’ and ceases its motion for a short time. Finally it recovers its 
complete shape, like the fruit of an eggplant, and gently begins to. swim with a 
definite rate. This fact also shows how soft and elastic itis. In a strict sense, how- 
ever, it does not always recover its former shape. For instance, when it was sub- 
jected to great pressure at the time of escaping its shape becomes like that of a snail, 
and in such a case after getting out it will be killed by the deformation. But even 
in the case of suddenly escaping, if the pressure and change in shape is not too great, 
it will swim freely soon after escaping. 
In the case of Zama the writer has given considerable attention to 
the method of escape of the spermatozoids and has observed the two 
methods described by Fujii. The first method of the gradual creeping 
out of the spermatozoid has been frequently observed in pollen tubes 
placed in sugar solution, but in almost all cases the tubes could be 
observed to have been broken previously, thus allowing the elastic 
spermatozoid to stretch out and creep through without actually pene- 
trating the membrane itself. In very numerous instances the extreme 
difficulty which the unwieldy spermatozoid has in overcoming slight 
obstruction has been observed; as, for instance, the difficulty of break- 
ing the plasma membrane of the pollen tube described above (p. 53). 
In Zamia, where the cellulose wall of the pollen tube is quite thick, the 
writer is inclined to believe that it would be impossible for them to 
penetrate the wall in thismanner. The second mode of escape by the 
sudden rupture of the pollen tubes is very commonly observed. At 
the time of maturity the tubes seem to be under great tension and a 
slight touch serves to cause them to burst and discharge their contents 
along with the spermatozoids as described in the writer’s second pre- 
liminary paper (123, p. 18). This method of escape in: Zama would 
seem unquestionably to be the one normally occurring in the process 
of fecundation, as described hereafter. 
