Observations on the Life-Cycle of Helkesimastix fsecicola. 363 



was almost square, the whole zygote, with its two flagella trailing along 

 near the outer sides, having almost the appearance of a procession banner 

 (fig. 47). (At a later stage the body becomes more definitely rectangular and 

 banner-like.) In this particular instance the zygote remained thus for a 

 couple of minutes or so, moving along steadily, the two " halves " with 

 their flagella at times approximating slightly, causing the common cytoplasm 

 to sag, as it were, just as a banner does when its pole bearers do not keep 

 their line. Now and again the zygote turned on its side, when it appeared 

 as in fig. 41. At length it altered again completely, a portion of the body, 

 apparently about a third of the bulk, advancing quickly in front of the 

 remainder (fig. 48), until the two portions were only connected by a very 

 narrow thread of cytoplasm, which was at first extended along and in contact 

 with, the greater part of the flagellum (fig. 49). We have no doubt that in 

 this remarkable dissociation of the zygote into two portions, one nucleus goes 

 with each half, just as the origin and proximal part of the flagellum can 

 clearly be seen to do. Unfortunately, we could not make out the nuclei at 

 all during these living observations of the conjugation-processes ; this was 

 due partly to the fact that in the earlier stages the conjugating pairs are very 

 active and constantly undergoing form-changes, and partly because, in the later 

 stages, the nuclei are most probably undergoing maturation prior to nuclear 

 fusion. This separation, which may amount almost to disruption, of the 

 common cytoplasm into two portions reminds us of the behaviour of the 

 protoplasm of Gercomonas (Gercobodo) above alluded to, but in Helkesimastix 

 it is not a passive leaving behind of a certain amount of protoplasm, but a 

 separation actively brought about by a difference in behaviour of the two 

 gametic energids. Here, again, in more than one instance (cf. fig. 54), we felt 

 sure that actual rupture was going to occur, but we have observed this remark- 

 able process on several occasions and the two halves never broke loose. 

 To return to our particular zygote, the small leading portion suddenly turned 

 right round, its flagellum becoming at the same time mostly free from the 

 cytoplasmic thread (fig. 50), and then joined up again to the main portion 

 (figs. 51 and 52). The zygote next assumed the form of a pear (fig. 53), 

 and after another minute or less the stage of fig. 45 was repeated, with the 

 difference that the smaller half was this time in front. The hinder part then 

 " slithered " up along the other and the banner form was again arrived at. 



All the above changes took place in a period of about 14 minutes from the 

 instant of first union. This time the banner was fairly permanent, and after 

 following it for a little while longer we left it, as we knew exactly what the 

 subsequent behaviour would be from numerous earlier observations. The 

 above described remarkable behaviour of the two conjugants — or, at least, of 



