THE LARGE GROUP OF THE SMALLEST OI\(;\Ms\is i:..-, 



vacuole, called the contractile vacuole, rhythmically collects and expels 

 fluid. The function of the contractile vacuole may he to eliminate 

 wastes from the cell, or it may have a hydrostatic function, that is, 

 it may control the amount of water contained in the ccjl. Food 

 particles are actually ingested or taken into the cell by the proto- 

 plasm which flows around the food, engulfs it, and then surrounds it 

 with digestive fluids in a food vacuole. 



A recent series of observations by Mast and Hanliart ' indicate 

 that the Ameba selects certain kinds of food, ])referring, for instance, 

 Chilomonas to Monas, although both are flagellates of about the 

 same size, form, and activity. It was further sliown that Monas 

 was not digested in the food vacuoles, while Chilajnonas was, and 

 also, some organisms, such as mold spores, certain algae, and other 

 flagellates, might be eaten but were not digested. 



The process of constructive and destructive metabolism may take 

 place in a single cell. Indigestible waste materials are pa.s.sed out 

 any^vhere from the surface 

 of the cell body, while 

 respiration takes place by 

 means of an osmotic ex- 

 change of the gases, oxy- 

 gen and carbon dioxide, 

 through the cell mem- 

 brane. 



As a result of the taking 

 of food, the cell gradually 

 increases in size and then 

 divides by a process known 

 as binary fission. Accord- 

 ing to a recent study by 

 Chalkley and Daniel - the 

 division of the nucleus 

 shows the typical stages 

 of mitotic division, the 



entire process lasting, under normal temperature conditions, about 

 half an hour. During the process the Ameba is quiescent and the 



late prophorse. 



mid- anaphase 



Gccriy anaphase 



•metaphose 



Mitotic division in the nucleus of Vruflia. i, After 

 GliiilklcN ;uni Daniel. ' 



iMast, S. 0., and Hanhart, W. L., " Feedins, Digestion, 

 (Leidy)." Phusiol. -Zool.. Vol. 8, lO.'?."). Pp. 2,5,5-272. 



-C 

 and the 

 Pp. 592-619. 



and StarviiliiiM in .■inwrbii pmlrw 



Iv)." Ph„.no}. 'Zool.. Vol 8. \9^r,. Pp. 2,5,5-272. ,i„„,vll 



Chalkley, H. W.. and Daniel. G. E.. "The Relation between the lorn, of he I. v .« r 1 

 the Nuclear Pha.ses of Division in Amoeba protcu.. (Leidy). Phmol. looU \o\. rt. !..,«•«. 



