110 BIOLOGY: GENERAL AND MEDICAL 



more difficult for the highly evolved organism to survive 

 in the general struggle for existence. 



The foreshadowing of organs elementary organs 

 are to be found among the protozoa and indicate that 

 these lowly organisms are subject to perhaps as much 

 specialization as is compatible with their unicellular 

 simplicity. 



Thus from the protamceba and amoeba whose shapes 

 can scarcely be regarded as fixed, and which consist of 

 plastic masses of protoplasmic jelly, we pass to higher 

 amceba that cover themselves with more or less elaborate 



Fia. 33. Amoeba proteus (magnified). The largest sphere is the contractile 

 vacuole; the smaller is the nucleus. A large diatom is seen on the left, and 

 numerous paraplasmic granules are scattered through the protoplasm. 

 (Masterman.) 



cases composed of minute particles of mineral substance, 

 and then to the foraminifera in which the body substance 

 is surrounded by fantastic calcareous shells through 

 fixed openings in which the pseudopods may be pro- 

 truded. We next pass to other forms in which the 

 development of the cell wall occurs as a hyaline but rigid 

 cuticle giving permanent form to the organism as in 

 Paramcecium, Vorticella, Epistylus, Stentor, etc. 



In the flagellates and ciliates we find the cuticular 

 cell wall perforated by many minute openings through 

 which special rigid protoplasmic threads project for 



