274 Wager.—On the Fertilization 
in the periplasm it is often elongated; and I have sometimes 
seen more than one nucleus in the periplasm elongated in 
the direction of the coenocentrum: but so far as I have been 
able to observe, only one nucleus actually comes into contact 
with it. The ooplasm at this stage is finely vacuolate and 
possesses in consequence a very distinct foam-structure 
( Fi g- 5 )- 
The fertilizing tube penetrates the oogonium at the place 
where the receptive papilla is formed. It forms at first 
a thin-walled spherical or oval sac in contact with the peri¬ 
plasm (Figs. 4, 5). It then penetrates the oosphere by means 
of a thin-walled tubular portion which is pushed out at its 
apex (Fig. 7). The fertilizing tube then presents a charac¬ 
teristic appearance, consisting of a thin-walled tubular portion 
in the oosphere and a slightly expanded, more or less 
spherical portion, in the periplasm. There are no nuclei in 
the tube when it is first formed, but before it has pushed 
itself into the oosphere, one nucleus from the antheridium 
passes into it, and as it penetrates the oosphere a second 
nucleus may pass into it (Fig. 7). 
Just before it passes into the fertilizing tube, the anther- 
idial nucleus changes its shape, becoming slightly elongated 
and often pointed at the anterior end (Fig. 4); this ap¬ 
parently enables it to pass more easily through the narrow 
opening which leads from the antheridium into the fertilizing 
tube. 
When the apex of the fertilizing tube comes into the 
neighbourhood of the central mass, with which the female 
nucleus is in contact, it opens and the male nucleus passes 
through the aperture into the oosphere and comes into contact 
with the coenocentrum (Figs. 7, 8). The male nucleus is 
slightly smaller than the female nucleus and stains differently 
in the carmine-nigrosin stain; the male nucleus is stained 
red, the female nucleus blue. They come into close contact, 
but do not fuse at once; they gradually increase in size, the 
male more rapidly than the female, until they are approxi¬ 
mately equal, and then separate to opposite sides of the 
