569 
Trow. — On Fertilization in the Saprolegnieae. 
Achlya De B ary ana. 
Fig. 14. Section of a young oogonium. Basal wall not yet formed. 
Fig. 15. Median section of an oogonium and antheridium. All the nuclei in mitosis, excepting 
one or two which appear to be undergoing degeneration. 
Fig. 16. Section of an oogonium with nuclei in mitosis. Nuclear figures somewhat irregular, 
suggesting a preparation for a second mitosis. 
Fig. 17. Thin layer stage in development of the oogonium. The nuclei are either undergoing 
degeneration or are in the prophases of the second division. The two nuclei in the antheridium are 
in the metaphase stage of the first mitosis — one is seen in a profile, the other in a polar view. See 
text, pp. 553-4- 
Fig. 18 1 +2+6+7+8+9+i2+i7 s h ows sections or portions of sections through one oogonium studied 
very thoroughly in a series of seventeen sections. The indices represent the numbers of the sections. 
Some of the nuclei are undergoing a second mitosis. The centrosomes and astrospheres make their 
first appearance at the poles of the spindles. Many nuclei are undergoing degeneration. See text, 
pp. 554-6. 
Fig. 19. Section through an oogonium at the commencement of the formation of the ‘ origins.’ 
Four origins are shown, each with a centrosome and astrosphere. A nucleus is present in each, too, 
but is only shown in a. There is a small supernumerary nucleus in d. 
Fig. 20. Tangential section of an oogonium which contained four uninucleate 4 origins.’ At a 
lower focus the two origins of this section were continuous. The nuclei of the antheridium are in 
the metaphase of the second mitosis. 
Fig. 21. Radial section of an oogonium with old origins. Mitoses completed in antheridia. 
Commencement of the formation of the ovocentrum. The nucleus has now no central chromatic 
mass. The centrosomes and astrospheres are very obvious structures. 
Fig. 22. Small portion of an oogonium with the adjacent antheridium, drawn to show a typical 
oosphere. Seventeen similar ones were observed in a series of six sections, but fertilization-tubes 
were absent. 
Fig. 23. Section of an oosphere at the moment of fertilization. A gonoplasm is present in the 
form of a thin strand which precedes the sperm-nucleus. The nucleus of the oosphere was in 
the adjacent section. 
Fig. 24. Two serial sections of a small part of one oogonium showing the fertilization of one 
oosphere. The entry of the fertilization-tube and sperm-nucleus is shown in a. The median section 
of the oosphere is shown in b, the nucleus, however, not being inserted. 
Fig. 25. Median section of a young oospore, showing female nucleus, centrosome, and astrosphere, 
the entry of the sperm-nucleus and the presence of a receptive spot. 
Fig. 26. Portion of a section of an oogonium and antheridium showing the fertilization of two 
oospheres. In a the sperm-nucleus obscures the centrosome situated below or behind it. A portion 
of the ovocentrum is seen, but the female nucleus was in the adjacent section. In b the sperm- 
nucleus has apparently taken a tangential course through the oosphere. 
Fig. 27. Tangential section of an oospore. At a , the male centrosome and astrosphere 
imbedded in the ooplasm ; at b, the male centrosome and astrosphere without the ooplasm ; at c, the 
associated male nucleus with the position of a portion of the astrosphere indicated. 
Fig. 28. Fertilized oospheres, the gameto-nuclei being accompanied by centrosomes and 
astrospheres. Rays of male astrospheres directed outwards. 
Fig. 29. Young oospores, in which the wall is clearly visible. The mode of attachment of the 
fertilization-tubes illustrated. The rays of the male astrospheres are directed outwards. 
Fig. 30. Young oospore. The centrosomes and astrospheres have disappeared and the ovocentrum 
is relatively small, but still includes the two gameto-nuclei. 
Fig. 31. Portion of a section of an oogonium with two binucleate oospores. The ovocentra 
have entirely disappeared, and the nuclei no longer occupy a central position. Deeply staining 
granules make their appearance in the protoplasm. 
Fig. 32. Section through a portion of an oogonium showing three oospores with conjugating 
gameto-nuclei. The chromosomes of the nuclei appear to be still in evidence. The granules in the 
protoplasm are very conspicuous. In two of the oospores the nuclei are alone represented in full. 
Fig- 33- Section through an oospore which contained two sperm-nuclei. The female nucleus was 
in the adjacent section. 
Fig. 34. An anomalous binucleate oosphere, one of three discovered in one oogonium. 
