Observations on the Life-Cycle of Helkesimastix fgecicola. 367 



proportion only of the total number of flagellates present. We have been 

 able, on several occasions recently, to follow the further behaviour of these 

 forms, and have ascertained the important fact that they always divide, and 

 never become rounded-off and form cysts. Moreover, we have observed a 

 certain number of these forms which were very large and possessed not two, 

 but three, or even four or five flagella (and nuclei, as ascertained from 

 permanent preparations). We have seen an individual with three flagella, 

 and also one with five, actually divide into two rather unequal portions ; in 

 the former case, one half had two flagella and the other one, and in the latter 

 case, one had three and the other two flagella (and nuclei). 



We will assume, for the present, that these forms represent a union of two 

 or more individuals, rather than a long-delayed division.* When we first 

 observed the isolated instances of biflagellate forms in this strain, we con- 

 sidered that they represented true syngamy, which, although occurring very 

 rarely was apparently still " latent." We now know (1) that these " unions " 

 may be either binary or multiple, apparently more or less indifferently ; 



(2) that these forms always divide, the nuclei and flagella being apportioned 

 out, often unequally, between the two halves, and that they never proceed to 

 form cysts— the invariable sequel, normally, to conjugation in Helkesimastix ; 



(3) and, lastly, that these forms, or the products of their division, are equally 

 incapable of persisting ultimately (unless, of course, they are transferred to 

 fresh medium). Hence, we feel certain that none of these unions represent 

 true syngamy. Bearing in mind the extremely plastic character of the 

 cytoplasm of this creature, we consider these unions are due to physical, 

 rather than " vital " factors, and result from continued cultivation and the 

 condition of the culture at the time. 



In our opinion, these peculiar cases do not invalidate the following 

 general conclusion which we wish to draw from our observations on this 

 non-conjugating strain. The "intensive" culture of this flagellate has 

 resulted in the loss of the power to undergo true syngamy and to form cysts. 

 The further existence of this " strain " is now dependent on continued 

 transference to fresh " constant " medium. Minchin, in his ' Introduction 

 to the Protozoa' (London, Arnold, 1912), in the chapter on "Syngamy and 

 Sex," has pointed out (p. 161) that " intensive culture, whether artificial or 



* We cannot yet write with certainty upon this point, because we think, from the 

 evidence obtained so far, it is possible that these forms represent a long-drawn-out mode 

 of division, due to the effect of the cultural conditions, in which the nucleus and 

 tlagellum divide, it may be more than once, before the cytoplasm does. There are other 

 cases known of a corresponding behaviour under conditions which are probably not 

 quite normal ; an example which is particularly interesting in relation to the present 

 discussion is that of multiple longitudinal fission in certain lethal trypanosomes. 



