Observations on the Life-Cycle of Helkesimastix fsecicola. 361 



axis, rather than transverse. This may represent a more primitive mode, 

 which has been largely relinquished in favour of the other. 



Syngamy. — In a fresh culture (either agar-plate or observation-preparation), 

 after the flagellates have once emerged from their cysts, multiplication goes 

 on, often at first with amazing rapidity, for two days or so, until by about the 

 third day — or sometimes even earlier — an epidemic of conjugation sets in. 

 The only important point in the whole life-cycle in regard to which we are 

 not yet certain is whether definite conjugating individuals, gametes, morpho- 

 logically distinctive from the usual forms, are developed, and, if they are, 

 whether these are anisogamous or not. Our difficulty arises from the fact 

 that in a culture in which conjugation is beginning, the flagellates present 

 show more or less the customary variation in size and form ; and, further, we 

 have not yet succeeded in seeing two individuals actually come together and 

 unite. In most of the cultures in which we have observed conjugation, the 

 majority of the individuals belong to one of two slightly different types. 

 One of these is rather characteristic and distinctive, we think, of this 

 period. It has the posterior end of the body gradually tapering and always 

 turned definitely to one side (figs. 34, 35), usually, though not invariably, 

 the right side, when the flagellum is dorsal or uppermost. The curved 

 tail-portion differs from the irregular extension sometimes seen at the hinder 

 end in ordinary individuals (cf. fig. 11), in being fairly constant and not so 

 changeable or metabolic, now retracted and now drawn out, as in that 

 case. The other type is distinctly smaller, but is not so readily distinguishable 

 from an ordinary individual (fig. 36) ; it is oval in shape, and the hinder end 

 is usually more bluntly rounded. 



In an observation-preparation in which syngamy has begun, two individuals 

 are often noticed to come into contact and glide along together for a short 

 while (fig. 37). The members of such a pair are very frequently — though, 

 again, not invariably — of the two distinct forms just noted. The larger one 

 of the two often appears to stick, or become attached to the other by its 

 curved, hinder end (fig. 38) ; when this happens, both individuals get very 

 excited and actively jerk themselves about for a moment or two ; then they 

 will either separate abruptly or glide along together for a short distance 

 again, and then move apart. Unfortunately, we have never seen this process 

 followed by actual union, and therefore cannot say whether it represents a 

 tentative seeking out of each other by definite gametes. Only in one case, 

 up to the present, have we caught the two gametes in close contact, with the 

 body-protoplasm of each still separate just for an instant before joining up 

 (fig. 39) ; and, in this case, so far as could be gathered from our momentary 

 impression before the two protoplasmic masses ran together, as it were, into 



