AMCEBA 133 



tance of 20 cm. during the twenty-four hours. On the 

 introduction of water-weeds into the vessel the Pelomyxse 

 were seen to crawl up them during the night, and on being 

 suddenly exposed to bright sunlight they contracted them- 

 selves into balls and dropped off the weed to the bottom of 

 the vessel, where they hid themselves under the mud. But 

 after the water-weed had been in the vessel for some time the 

 Pelomyxse no longer left the mud but stayed buried in it both 

 by day and night. It would seem that, before the introduction 

 of the water-plant, the water became deficient in oxygen, and 

 that the deficiency was greatest in the mud at the bottom of 

 the vessel. During the day the animalcule's aversion to light 

 proved stronger than its intolerance of an insufficient supply 

 of oxygen, so it remained buried in the mud, but during the 

 night left its hiding place in search of oxygen. When the 

 whole contents of the vessel became appropriately oxygenated 

 the migration ceased. 



Thus Amoeba, simple as its constitution is, exhibits the 

 characteristic vital phenomena of irritability, automatism, 

 assimilation, and excretion. We cannot doubt that it is also 

 metabolic. The pseudopodial movements are manifestations 

 of energy ; they imply waste of material, and we can infer 

 from the fact that the animalcule takes in and digests food 

 that the waste of its substance is made good by the elaborated 

 products of digestion. In so small an organism the actual 

 processes of waste and repair cannot be followed out in detail, 

 none the less we can assert that they are performed. So, too, 

 we can assert that the Amoeba is respiratory, that the energy 

 exhibited in pseudopodial movement is the result of the 

 oxidation of the tissues, and that one of the waste products 

 is carbon dioxide. There is no definite respiratory organ, 

 unless, indeed, the contractile vacuole functions as such, and 

 the amount of carbonic acid gas given off is too small to be 

 collected and measured. But the same observation which 

 showed that Pelomyxa is sensitive to light shows also that it 

 requires oxygen. 



Lastly, Amoeba is reproductive. It propagates its kind 

 in the simplest and most primitive manner by binary fission. 

 Seeing how common an object of study Amoeba is, it is re- 

 markable that the process of binary fission is but rarely 

 observed, and that even now we are not sure whether mitotic 



