Observations on the Life-Cycle of Helkesimastix faecicola. 357 



an individual was moving sluggishly along, the posterior, plastic part of the 

 body would come into contact at some point with a small extraneous 

 particle. A small portion of the protoplasm of the flagellate in the imme- 

 diate neighbourhood of the point of contact would remain adherent to the 

 still stationary particle for a few seconds, gradually engulfing it, while the 

 Gercomonas moved calmly on. Thus most of the body was quickly separated 

 from the small portion of cytoplasm remaining behind, until often only an 

 extremely thin thread or line of protoplasmic substance still joined the two 

 parts ; this thread might be as long as the whole body of the flagellate. 

 Suddenly the tension of the connecting thread overcame the resistance of 

 the stationary particle, and the latter, together with the small portion of 

 protoplasm surrounding it, was safely hauled up again into the main body. 

 We often thought the thread must break, but it never did ! 



As our new flagellate shows a resemblance in some respects to Gercomonas, 

 we have watched particularly for the occurrence of anything corresponding, 

 which, however, we have never seen, although analogous appearances are seen 

 during conjugation (cf. below). We have never been able to satisfy ourselves 

 that Helkesimastix does engulf solid particles at the hinder, plastic end, but 

 do not deny the possibility of it doing so. We certainly consider, however, 

 that its principal mode of nutrition is by osmosis. The natural habitat of 

 the creature, namely, moist dung, is, of course, rich in organic matter in 

 solution, when the bacteria have been active for a little time. In Helkesimastix, 

 therefore, we have an instance of a form which is, at all events, mainly 

 saprozoic. 



The contractile vacuole is usually small, that is to say, it contracts before 

 it attains a large size. It is generally situated in the hinder part of the body, 

 to one side (figs. 8, 10). Now and again, however, owing doubtless to some 

 condition of the medium, the contractile vacuole becomes very large (fig. 15). 

 Immediately after it has ruptured the protoplasmic wall and its contents have 

 passed out to the exterior, the body of the flagellate presents for a short time 

 the curious appearance of fig. 16 ; the hinder end is forked, like the two arms 

 of a V. After a little while it becomes triangular (fig. 17), and ultimately 

 assumes again its normal shape. 



Another point illustrating the looseness or plasticity of the body is a method 

 of turning round often shown by a sluggishly moving individual. It will come 

 to rest, and the body becomes more ovoid (fig. 18). Then the side with which 

 the flagellum is in close contact begins to show what we term " working " 

 movements ; at first the peripheral protoplasm moves in slow, short, irregular 

 waves to and fro, the line both of the contiguous part of the flagellum and of 

 the row of granules (if these are present) becoming meanwhile indented and 



