GYMNOSPERMS. 159 
During the final stages in the development of the spermatozoid the 
proximal end of the pollen tube, which is still capped by the exine of 
the spore, grows downward into the prothallial cavity as in Zama 
(Fig. 65, A). This cavity in Cycas, according to Ikeno, is filled 
with a watery fluid derived largely from the archegonia, and in which 
the spermatozoids swim on escaping from the pollen tube. Webber 
is of the opinion that in Zamdza this fluid is derived largely from the 
pollen tube. 
The spermatozoids in Cycas, on escaping from the pollen tube, swim 
about rapidly, and in a short 
time penetrate the egg. 
That part of the egg at which 
a spermatozoid enters is de- 
pressed, giving the impres- 
sion that it came against the 
egg with some force. The 
nucleus of the spermatozoid 
now escapes from its cyto- 
plasmic mantle and migrates 
toward the nucleus of the 
egg. The cytoplasm and 
blepharoplast are left in the 
upper part of the egg as in 
Zamia (Fig. 66, A, B), 
where they undergo disor- B 
ganization. It frequently Fic. 66.—Fecundation of egg-cells in Zamia.—(After 
Webber.) 
happens that several sperm= A, egg-cell immediately after coming together of male and 
atozoids reach the egg, but, female nuclei; the ciliferous band of fecundating sper- 
1 ly trat matozoid lies in upper end of egg; a second *spermato- 
as a rule, only one penetrates zoid trying to gain entrance is shown at apex of egg. 
into its interior, the others BB, similar to A, but showing longitudinal section of ciliferous 
remaining at the surface,  "=nd im upper end of cee. 
Whether more than one male nucleus ever fuses with the egg-nucleus 
is not known. 
When male and female nuclei come in contact they are readily 
distinguished from each other, the male being smaller, with a more 
finely granular threadwork. Both are in the resting stage. The male 
nucleus seems to press against the female, forming a depression in the 
latter. Inashort time the male nucleus is completely imbedded within 
the egg-nucleus; the membrane of the male nucleus disappears, and 
the two nuclei fuse so completely that the fusion nucleus can scarcely 
be distinguished from an unfecundated nucleus of the egg. 
