PROTOPLASM OF PROTOZOA 67 



the Protozoa, is surrounded by a limiting surface membrane which may 

 be demonstrated in many forms by the usual cytological techniques (see, 

 for instance, Chalkley, 1936). In addition, experimental studies on the 

 living nucleus by Kite (1913), Chambers (1924), C. V. Taylor (1920), 

 and many others have substantiated the view of the presence of a defi- 

 nite nuclear membrane, often extremely thin, but usually composed of a 

 moderately tough, solid substance, which, upon rupture of the surface 

 of the organism, may preserve the integrity of the nucleus for a consider- 

 able time. Seifriz (1936) reports that the nuclear membrane of Amoeba 

 may be readily removed by microneedles, following coagulation of the 

 nucleus as a whole. 



Morita and Chambers (1929) have shown that the nuclear membrane 

 of Amoeba is permeable to acid, while the general body surface of the 

 animal is not. 



King and Beams (1937) report that the macronucleus of F. caudatum 

 in the vegetative stage was greatly stretched by centrifugation. In some 

 specimens it was separated into a relatively heavy chromatic portion and 

 a relatively hght achromatic portion. Animals with their macronucleus 

 separated in this way were able to live and carry on apparently normal 

 metabolic processes. Here it is evident that a mechanical disruption of 

 the macronucleus did not cause a marked physical change of the cyto- 

 plasm, as often happens when the nucleus is punctured or cut by a needle 

 (Kite, 1913; Peebles, 1912). King and Beams were unable to differenti- 

 ate a limiting membrane surrounding the two separated portions of the 

 macronucleus, and, if present, it must have been of ultramicroscopic di- 

 mensions. 



Luyet and Gehenio (1935) were unable to demonstrate a definite 

 membrane surrounding the macronucleus of P. caudatum by means of 

 ultra-violet absorption methods. 



Whatever, in the final analysis, the physical structure of such ultra- 

 microscopic nuclear membranes may prove to be, it will probably in- 

 volve a special molecular behavior, characteristic of surfaces much like 

 that which is thought to occur between nonliving immiscible fluids. 



3. Contractile vacuole. — For the early literature dealing with the long- 

 disputed question of the presence or absence of a permanent membrane 

 surrounding the contractile vacuole in Protozoa, the reader is referred to 

 the works of C. V. Taylor (1923), Lloyd (1928), Howland (1924a), 



