ALBUGO (CYSTOPUS). 99 
nucleus. Swingle (’98) called attention to this body in A. candida, 
which he was inclined to regard as an organ of the odgonium, taking 
some part in the delimination of the egg and the fusion of the male 
and female nuclei. A similar body has been observed in A. d/¢¢7, A. 
tragopogonis, and A. portulacee, by Stevens (’99), who proposed 
for it the name ‘‘ceenocentrum.” In A. 4/z¢2, in which it was 
described as structureless and unchanging, this body does not seem to 
be so intimately associated with the sexual nuclei as in A. candida, as 
noted by Wagerand Davis. In A. ¢ragopogonzs it occupies an interme- 
diate position in size between that in A. d/¢t¢ and A. candida, where 
it is largest. According to Davis’s figures the female nucleus does 
not become embedded in the body in question. In A. candida this 
body disappears during the union of the sexual nuclei or a little later. 
There is no doubt that these observers refer to the same phenome- 
non, which is the expression of a specialized and tolerably well differ- 
entiated portion of the cytoplasm of the oogonium. It may have to do 
in some way with the delimination of the egg-cell and, possibly, with 
the union of the sexual nuclei, but it certainly can not be regarded as 
an organ of the cell or of the odgonium with morphological rank. 
Stevens (’o1) regards this body as nutritive in character and exerting 
a chemotactic stimulus upon the sexual nuclei. 
During the changes just described the nuclei of the antheridium have 
been undergoing division, and their number is now about twice that at 
the beginning. The conjugation-tube has grown and pushed its way 
through the periplasm into the plasma of the egg. A single nucleus 
and a small quantity of densely staining cytoplasm pass from the 
antheridium into the conjugation-tube to its apex (Fig. 35, D). The 
tube now grows toward the centet of the oosphere, around which a 
plasma membrane has not yet been formed (Fig. 35, E). The dense 
mass of cytoplasm in the end of the tube becomes reduced in amount, 
having been used up probably to form the new growing wall (Wager, 
’96, p. 330). The growth of the conjugation-tube continues until it 
comes into contact with the central mass of dense cytoplasm (cceno- 
centrum) referred to in the preceding paragraphs. As soon as the end 
of the tube comes into contact with the nucleus of the egg the male 
nucleus is expelled and the tube immediately contracts, or rather col- 
lapses, and is withdrawn from or absorbed by the odsphere, leaving a 
large vacuole to mark its position (Fig. 36, F, a). The two nuclei are 
thus left in close contact with each other, the male being slightly smaller 
than the female (Fig. 36, F). A delicate membrane, the plasma 
membrane, now becomes visible around the oosphere, separating it 
from the dense surrounding cytoplasm, the periplasm. From Davis’s 
