Observations on the Life- Cycle of Helkesimastix fsecicola, 355 



more convinced of this because we had previously seen the excystation of a 

 species of Bodo from other dung-cultures, and in that case the rupture of the 

 cyst-wall was very evident, and when the Bodo had moved away the empty 

 cyst-wall was left behind. To return to Helkesimastix, when a sphere from 

 which the cyst-wall had disappeared was watched it was seen gradually to 

 change its shape, and in about seven minutes had elongated somewhat and 

 become ovoid (fig. 5). Near one extremity a small vacuole had made its 

 appearance, which represented the contractile vacuole ; active metabolism 

 had again begun. Very slight, spasmodic movements were noticed at 

 intervals, and then suddenly it was seen that a very short, delicate 

 flagellum was present, apparently emerging from about the middle of the 

 body (fig. 6). This waved slowly to and fro, though we do not feel at all 

 certain that it was causing the jerky movements. The flagellum could at 

 first be made out only when it was projecting from the side of the creature, 

 and not when it lay over the body-protoplasm. Meanwhile the flagellate was 

 growing in size rapidly, and five or six minutes later it appeared as in fig. 7 : 

 the flagellum had lengthened considerably and was more prominent and 

 stouter, and its point of origin was now near to the anterior end. The 

 nucleus had doubtless also passed towards the anterior end, but unfortunately 

 it could not be clearly made out ; this was owing partly to the jerky move- 

 ments and partly to the fact that the protoplasm was becoming very granular. 

 The jerky, to and fro movements of the body, producing no displacement of 

 the creature, are very characteristic of certain phases ; we describe them as 

 " knicking " movements (cf. below, p. 358). Ten minutes later the flagellate 

 was beginning to make short, gliding movements of progression, and these 

 alternated for some time with the knicking movements until, after about an 

 hour, it moved steadily for the first time out of the field of vision. 



During this period the same process had been going on throughout the 

 preparation, and many actively gliding individuals were now present. These 

 were all growing rapidly before beginning to multiply, and attained a size 

 considerably larger than the average individual size found later on ; the 

 protoplasm was usually full of refringent granules. 



Form and Structure. — The body of the ordinary active individual of 

 Helkesimastix fcecicola is typically elongated and fairly cylindrical, with one 

 end (the anterior one) bluntly rounded, the other (posterior) one tapering 

 away more and being at times somewhat pointed (figs. 8, 10, 13). The 

 broadest part of the body is generally nearer to the anterior end. "We can 

 most aptly compare the form with that of the fleshy part of a small carrot. 

 Sometimes the hinder extremity is drawn out into a narrow prolongation 

 (fig. 11). This hinder part of the body is often very plastic and irregular, 



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