370 Observations on the Life-Cycle o/Helkesimastix f'secicola. 



EXPLANATION OF FIGURES. 



All the drawings, with the exception of fig. 12, are from sketches made directly at the 

 time of the living observation. Fig. 12 is a camera lucida drawing of an individual fixed 

 with osmic acid vapour. The magnification throughout is approximately 2250 times 

 linear, arrived at after a comjmrison of other individuals fixed with osmic. We are 

 indebted to Miss Rhodes for kindly tinting and sharpening up the drawings. 



In our figures, we have shown the nucleus or omitted it, according as to whether we 

 were able to observe its position in the particular individual represented, or not. As 

 mentioned in the text, we were unable to make out satisfactorily the nuclei in life, in 

 the conjugating pairs. 



Note with regard to the flagellum : — As mentioned in the text, the length of the 

 fiagellum varies in individuals otherwise similar. In order to save space, we have drawn 

 the flagellum usually short, except in fig. 10 ; the flagellum of the individual of fig. 12 is, 

 of course, natural length. 



Plate 13. 



Figs. 1-3.— Cysts. 



Figs. 4-7. — Excystation and the development of the flagellum. 

 Figs. 8-11. — Different forms of individuals. 



Fig. 12. — Individual fixed with osmic acid vapour, to show that the flagellum is not 



actually attached by any membrane to the body. 

 Figs. 13 and 14. — To illustrate the behaviour of the flagellum in turning of the body. 

 Figs. 15-17.- — Rupture of a large contractile vacuole and form-changes of the body. 

 Figs. 18-21. — To illustrate a mode of turning of a stationary individual (see text). 

 Figs. 22-26, 27-31, and 32 and 33. — Different instances of division (binary fission). 



Plate 14. 



Figs. 34-36. — Different fornis predominating in a culture about to start conjugation. 

 Figs. 37-62. — The whole process of conjugation (syngamy), showing the different form- 



changes during the progress of the fusion. 

 Figs. 63-67. — The gradual contraction of the body and absorption of the two flagella of 



the zygote, prior to encystment. 

 Figs. 68 and 69. — The cysts as first formed, so-called " shrinkage " cysts, with a vacuole 



or space of varying size. 



