Reproduction of Cystopus Candidus , Ldv. 341 
Fig. 13. Oogonium showing ovum-nucleus with its deeply stained mass of 
protoplasm, and a fertilizing tube with nucleus at the apex. Owing to the 
action of re-agents the fertilizing tube is shown slightly contracted away from the 
protoplasm into which it is pressing. The central mass of protoplasm which will 
become the oosphere shows, as well as in previous sections, a very characteristic 
foam-structure. 
Fig. 14. Later stage than Fig. 13. The apical wall of the fertilizing tube is 
now becoming very thin, and the tube itself is expanding at the apex into a bladder- 
like structure. The wall of oosphere has not yet begun to form. 
Figs. 15 and 16. Two successive sections of the same oogonium, showing the 
fertilizing tube in contact with the central or ovum nucleus. 
Fig. 15. Ovum nucleus shown, and fertilizing tube which has contracted away 
from it, probably owing to the action of re-agents. 
Fig. 16. Shows the apex of the fertilizing tube with nucleus, the deeply stained 
mass of protoplasm in contact with the ovum nucleus is shown on the wall of the 
space produced by the contraction of the fertilizing tube. These two sections 
taken together show that the male nucleus is brought quite into contact with the 
ovum nucleus by means of the fertilizing tube. 
Fig. 17. Section showing the male and female nuclei in close contact with one 
another. The male nucleus is expelled from the fertilizing tube in some way, 
probably by a gradual thinning and ultimate rupturing of its apex, the fertilizing 
tube being immediately withdrawn, a large vacuole ( a ) being left to indicate the 
place where it was. The two nuclei in the egg are still surrounded by a dense mass 
of protoplasm. The wall of the oosphere can now be seen. 
Fig. 18. Portion of a section of an oogonium immediately after fertilization, 
showing the fertilizing tube withdrawn to the outside of the young oosphere, and 
presenting an appearance as if ruptured or disorganized at the apex. 
Fig. 19. An older oogonium with young oosphere showing the empty fertilizing 
tube on the outside of the latter. The antheridium contains still a small quantity 
of protoplasm, and a number of small degenerating nuclei. 
Fig. 20. Section of an oogonium at a later stage than Fig. 17, showing the 
nucleus of the oospore shortly after the fusion of the male and female nuclei. 
Two nucleoli can be seen, and the nucleus is of an oval shape and still surrounded 
by the dense mass of protoplasm. The wall of the oosphere, the exospore, is now 
distinctly visible. 
Fig. 21. Oospore nucleus at a later stage than in Fig. 20. It contains a con- 
siderable number of granules, probably chromosomes, and a very distinct nuclear 
membrane. It is surrounded by a small quantity of the dense deeply stained 
protoplasm only. As the latter disappears the nucleus takes a more intense stain 
and increases in size. The wall of the .oospore just begins to show the appearance 
of the columnar layer of the exospore. 
Fig. 22. Oogonium with oospore, slightly later stage. The columnar layer of 
the exospore is now visible as a number of minute projections on the inner wall. 
The chromosomes of the nucleus are contracting towards the centre, probably 
preparatory to division. 
Fig. 23. A still later stage of oospore formation. The columnar layer is more 
strongly developed. The endospore has not yet begun to develop. The chromo- 
somes are still more contracted towards the centre. An antheridium attached to the 
wall of the oogonium shows a number of small degenerating nuclei. The periplasm 
