46 PROTOPLASM OF PROTOZOA 



tures are similar to those which occur in the mitotic divisions of cells 

 of higher forms. For a discussion see Gray, 1931; Heilbrunn, 1928; 

 and Chambers, 1938. 



Properties of Protoplasm as Exhibited in Amoeba 



To obtain a concept of protoplasmic structure no better course can 

 be followed than to secure a microscope, some amoebae, and study them 

 under relatively high power. Efforts to obtain this information from the 

 literature alone often lead to confusion, because of the wide variety of 

 terminology used by the various workers on the structure of amoebae. 

 Careful microscopic examination of the protoplasm of Amoeba proteus 

 in locomotion will reveal that it is composed of an outer, thin, colorless, 

 hyaline layer which is for the most part optically structureless, and an 

 inner granular region which makes up the greater portion of the 

 animal. A detailed study of the granular portion will reveal that it is 

 composed of a colorless continuous phase (hyaloplasm), in which are 

 suspended crystals and granules of various sizes and shapes, nucleus, 

 food vacuoles, contractile vacuole, refractive bodies, oil globules, and 

 possibly other inclusions. Long intervals of observation on these struc- 

 tures will show that some of them seem to be permanent and self- 

 perpetuating while others are only transitory. The question that naturally 

 arises in this connection is, which are living and which are nonliving 

 bodies? A further discussion of this point will be given elsewhere. 



The question may now be asked, how are the various microscopically 

 visible inclusions of Amoeba protoplasm kept in suspension? This may 

 be because their density is only slightly different from that of the sur- 

 rounding protoplasm and because of the viscosity of the protoplasm. 

 Mast and Doyle (1935a) have presented evidence that the refractive 

 bodies, which are the heaviest inclusions of the protoplasm, are found 

 near the lower surface in living amoebae in which the protoplasmic vis- 

 cosity is low; that they are distributed by protoplasmic flow has been 

 demonstrated by Mast and Doyle (1935b). Upon centrifuging, the 

 cytoplasmic constituents of amoeba are layered out, in order of their 

 relative specific gravity, with the refractive granules at the centrifugal 

 pole. Upon recovery pseudopods form first at or near the lighter end, 

 and the heavy refractive bodies then flow forward followed by the other 

 layers of constituents until all are thoroughly mixed. 



