AN AQUATIC MYXOMYCBTE. 81 



oxygen-consumers is the chief. While not denying that the myxa- 

 moebae may be impelled to encyst from lack of food, or when the 

 temperature is too low, there is reason for ascribing these dormant 

 states chiefly to a lack of oxygen, since the myxamcebse may be re- 

 awakened to activity on the mere addition of pure water containing 

 oxygen, though the temperature (not too low) remains the same. 

 Beyond the fact that such cysts may lie unchanged for 12 or 14 days, 

 and then be restored to activity, I do not know how long they retain 

 their vitality. 



In fig. 21 (a) is a cyst kept under observation (with seven others) 

 for some time : after resting for two days, a minute drop of fresh 

 nutritive solution was added, and three hours later it and its com- 

 panions were beginning to germinate. The process (cf. fig. 21c and d) 

 is very simple, the extremely thin membrane opens by a minute pore, 

 evidently formed by the myxamceba itself, through which the whole of 

 the protoplasmic contents pass out as an extremely active myxamceba, 

 which soon shows the presence of a cilium. The pulsating vacuole is 

 formed before its escape ; the nucleus is evident all through the dor- 

 mant state : the flagellum seems to be protruded after the escape of 

 the myxamceba. In some cases the extremely fine colourless envelope 

 was dragged for a short distance by the myxamceba, but it soon fell 

 off, and the tiny round hole through which the contents had escaped 

 could then be detected. Such empty cysts were often to be seen in 

 certain cultures which had been allowed to dry up and were then 

 wetted, and as they increased the number of encysted myxarncebae 

 decreased. Moreover, it was by no means difficult to see the process 

 of escape of the contents, as in the specimen figured ; I have watched 

 the process from beginning to end at least five times. It only remains 

 to add that the free myxamceba may feed, grow and divide, or may 

 again encyst, according to circumstances ; or, finally, under certain con- 

 ditions, which I have failed to refer to anything external, the myxa- 

 moebse may commence to congregate in masses and subsequently form 

 plasmodia. I have failed to obtain satisfactory evidence as to the con- 

 stitution of the extremely thin wall of the cyst : it is, presumably, 

 cellulose, but its delicacy is such that reagents destroy every trace of it 

 before one can be assured of a colour reaction. It is not improbable 

 that this encysted stage is far commoner in myxamoebae than has 

 hitherto been supposed, for the very delicate transparent empty cases 

 are almost sure to be overlooked at first. 



G 



