398 



Mr. C. H. Martin. 



[May 10, 



initiate the formation of some substance by the bacteria toxic to the flagellate 

 and to which it reacts by encystation. But it is evidently useless attempting 

 to analyse the physiology of this phenomenon without a great deal more 

 experimental evidence than I have at present collected. 



I will only draw attention to one other feature in the physiology of these 

 cultures before proceeding with my account of the morphological features 

 presented in the formation of the zygote-cyst. On several occasions I have 

 attempted to make sub-cultures of this flagellate from flourishing cultures 

 in which few or no cysts were present. These cultures always failed. Whether 

 this failure was primarily due to a zoological or a bacteriological factor I am at 

 present unable to say, but sub-cultures made from the same primary cultures 

 at a later stage when the cysts had been formed were uniformly successful. 



The conjugation in this flagellate is probably isogamous, and there seems 

 to be a certain amount of evidence tending to show that the gametes are 

 characterised by a slightly larger size of body and by a slightly smaller 

 nucleus containing a relatively smaller caryosome. The gametes usually 

 contain quantities of ingested bacteria, and it would seem that this pro- 

 nounced trophic activity constantly precedes conjugation. The gametes seem 

 to come into contact laterally, and the zygote formed by their fusion swims 

 around actively for some time by means of its two flagella (figs. 10 and 11), 

 which seem to be always inserted near the same pole. The zygote now 

 grows in size, the growth appearing to be largely due to the formation of a 

 large vacuole in the posterior portion of the body. At a slightly later 

 stage this vacuole is found to be occupied by a solid round body, which I 

 am inclined to regard as a reserve-body (figs. 13, 14). The flagella now 

 disappear, and I have not yet succeeded in tracing the fate of the blepharo- 

 plasts in the later stages of the zygote. 



The zygote now secretes a wall, and presents a very characteristic 

 appearance with its two nuclei closely applied to the anterior wall of the 

 large vacuole containing the reserve-body. The reserve-body is best shown 

 in early cysts stained with iron-hasmatoxylin, which stains it a faint 

 yellowish colour. The ripe cysts can only be stained with great difficulty 

 with acid hsematoxylin. In these permanent preparations the reserve- 

 body cannot be seen (figs. 15, 16). The nuclei apparently now undergo 

 some process of reduction division, as is shown in figs. 13 and 14. But I 

 hope to return to this point in my final paper. The ripe zygote-cyst {vide 

 fig. 16) contains a single nucleus, the result of the fusion of the nuclei of 

 the two gametes. To the question of some of the peculiar features displayed 

 by this life-cycle, and the light which they may throw on the affinities of 

 this flagellate, I hope to return in my forthcoming paper. 



