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Dr. H. M. Woodcock and Mr. G. Lapage. 



fairly homogeneous, or contains fine granules. There is frequently, however, 

 a conspicuous, somewhat refringent grain, situated near the periphery 

 (Plate 13, figs. 1 and 2), but no vacuole is present. The nucleus can usually 

 be seen as a clearer area, and at times the contained karyosome can be 

 distinctly made out as a dull body in the centre. No division takes place 

 inside the cyst, which is therefore a resting or "Dauer" cyst and not a 

 multiplicative one. 



Excystation. — We have followed the process of excystation in cysts which 

 had been for about 22 hours in fresh medium (Liebig broth). This is not 

 quite the minimum period required, before the flagellate will emerge from its 

 cyst, for in this particular preparation some half-dozen individuals were 

 already active by this time, though the great majority were still encysted. 

 The period which must elapse depends, we consider, upon how soon the 

 multiplication of the active bacilli in the new environment has taken place 

 to a sufficient extent to produce, in sufficient quantity, the ferment or 

 chemical substance in solution which is either directly or indirectly the 

 cause of the dissolution of the cyst-wall. For we are strongly of opinion 

 that the explanation of both the encystment and the excystation of 

 Helkesimastix (and probably equally of other dung- and infusion-flagellates) 

 is to be found in the view put forward by Cropper and Drew* in their recent 

 important and suggestive work on the causative factors of the corresponding 

 phenomena in Amcebce. We hope to study our new flagellate from this 

 biological standpoint subsequently, and will here merely indicate in passing 

 certain facts we have observed which bear upon the question. We have found 

 excystation occurring only in those cultures, plates, or observation-prepara- 

 tions in which there was a plentiful development of an (or of more than one) 

 active, markedly aerobic bacillus, which we have not yet more closely deter- 

 mined. We have kept cysts in ordinary cover-slip preparations in different 

 media (the preparations being sealed, of course, to prevent evaporation), for 

 several days, without the emergence of any active individuals taking place ; 

 and in such preparations, the medium not being in contact with free air, no 

 noticeable development of active bacilli took place. 



In a cyst from which the flagellate is about to be liberated the wall is 

 noticed to become gradually less and less obvious, until at length one can no 

 longer say that there is any envelope present, apart from the delicate mem- 

 brane or pellicle limiting the body-protoplasm (fig. 4). There is no definite 

 rupture or bursting of the wall at any point, through which the flagellate 

 could pass out to the exterior ; in other words, when the creature has again 

 become active and moved off, there is no cyst-wall left behind. We were the 



* ' Researches on Induced Cell-reproduction in Amoebfe,' London, John Murray, 1914. 



