24 American Quarterly Microscopical Jotcrnal. 



the first formed on the filament, and appeared no different 

 from the others of the same age. Why did this change take 

 place ? If we accept M. Cornu's statement, that the new form 

 is provided with cilia, it would seem that the relation of this 

 outer wall to the zoospore is like that of the pericarp to the 

 seed. But in the specimens I examined with a magnifying 

 power of 750 diameters (Fig. 17) I in no case observed cilia, 

 and think that the slow oscillating movement which occurred 

 could have been caused by the slight change in temperature 

 from the inside of the spore-case to the surrounding liquid, 

 and the change may have taken place on account of the cell 

 wall becoming tough and distinct from the contained proto- 

 plasm, as these zoospores remained at rest much longer than 

 those which germinated without the change. As soon as the 

 sporangium was emptied, the plant commenced to swell up 



DESCRIPTION OF PLATE VI. 



Fig. I. Achlya sp. growing on a pine twig, natural size. 



Fig. 2. A short filament bearing oogonia, magnified 120 times. 



Fig. 3. Oogonium largely magnified, showing the fertilization of the contained 

 gonospheres. 



Figs. 4-10. Oogonium in different stages of development. 



Fig. II. A cylindrical, inter-filamental and spherical lateral oogonium on the 

 same plant. 



Fig. 12. Spores of sexual generation 20 hours from gonosphere. 



Figs. 13, 14. The same germinated. 



Fig. 15. Oogoxivxxa.oi Achlya polyandra. 



DESCRIPTION OF PLATE VII. ,i 



Figs. I, 2. Sporangia and zoospores of Achlya sp. 



Fig. 3. Germination of zoospores and formation of a second sporangium. 



Fig. 4. Branch of Monoblephans lateralis showing position of oogonia, mag- 

 nified 50 times. 



Fig. 5. Young oogonium showing the male organ. 



Figs. 6-7. Birth of the antherozoid. 



Fig. 8. Empty sack attached to the oogonium. 



Fig. 9. Antherozoid settled down after birth. 



Figs. 10-12. Amoeboid forms assumed. Fg. 12 was taken one hour and twenty 

 minutes from oogonium. 



Figs. 13-18. Antherozoid upon an oogonium. Figures made at intervals of 

 twenty minutes. 



Fig. 19. An oogonium showing the fertilization ot the gonospheres. 



Fig. 20. A rare and late form. 



Fig. 21, Oogonium showing the openings "in the membrane, also the attach- 

 ment of an empty antherozoid sac and antherozoid after performing fertilization. 



