178 Trow . — Observations on the Biology and 
EXPLANATION OF FIGURES IN PLATES 
VIII-X. 
Illustrating Mr. Trow’s paper on Achlya. 
The figures were traced with the camera lucida and the finer details filled in by 
free hand. Most of the work in karyology was actually carried out with the aid 
of Zeiss’s achromatic homogeneous immersion objective (N. A. 1*25) and 
compensating oculars. All the important results, however, were controlled by 
observations made with the 2 mm. apochromatic oil-immersion objective 
(N. A. 1.4). Artificial light was employed throughout for the study of the 
sections, which were of a uniform thickness of 7-5 /x. 
Abbreviations: — deg. n ., degenerate nucleus; f.g.n ., female gameto-nucleus ; 
m.g. male gameto-nucleus; f. /., fertilization-tube. 
Fig. 1. Habit of the plant growing on flies floating on water. Nat. size. 
Fig. 2. Sexual hyphae with young oogonia. Slightly magnified. 
Figs. 3-9. Stages in the development of the same oogonium and antheridium 
kept under constant observation for about eighteen hours, x 540. 
Figs. 10-26. Stages in the development of a second oogonium and antheridium 
kept under regular observation for fifteen days. The development of the oospheres 
and of the fertilization-tubes, and the maturation and germination of the oospores 
are represented in detail, x 540. 
Fig. 27. An oogonium, probably apogamous, with three germinating oospores, 
x 540- 
Fig. 28. An oospore, one of three in an oogonium, germinating and producing 
a mycelium without the intervention of sporangium-formation, x 17°. 
Figs. 29 and 30. An apogamous oogonium kept under regular observation for 
a month. 'Germination took place, but slowly. x 540. 
Fig. 31. A group of four zoospores, the nucleus and outline alone represented 
in one. x 1,200. 
Fig* 32. An oblique section of a sporangium. The spores had encysted within 
it, giving rise to a network of cell- walls, x 1,200. 
Fig* 33. A median section of a very young oogonium at the stage corresponding 
to that of Fig. 2. x 1,200. 
Fig. 34. A median section of an older oogonium at the stage corresponding to 
that of Fig. 3. x 1,200. 
Fig* 35* A median section of an oogonium at the stage corresponding to that 
of Fig. 7. x 1,200. 
Figs. 36-40. Small portions of sections of oogonia at the stage corresponding to 
that of Fig. 8. x 1,200. 
Figs. 41 and 42. Median sections of oogonia at the stage immediately preceding 
balling. Fig. 42 about an hour earlier than Fig. 41. x 1,200. 
