6 



THE PROTOZOA 



result of degeneration and specialization. These organisms do not 

 conform to the type of structure of the cell, as this word is usually 

 understood, since they do not exhibit, speaking generally, a division 

 of the living body substance into a nucleus distinct from the 

 cytoplasm ;* but the chromatin is distributed through the proto- 

 plasmic body in the condition of scattered lumps or granules 

 (" chromidia "), and in many cases it constitutes, apparently, the 

 whole or a very large proportion of the substance of the body. 



Fro. 2. Amoeba proteus. A, An individual in active . movement ; the arrows 

 indicate the direction of the currents in the protoplasm ; at r is seen a pseudo- 

 podium which is nearly completely retracted and has assumed a mulberry- 

 like appearance ; c.v., contractile vacuole ; /., fsecal matter extruded at the 

 end of the body posterior in movement ; the nucleus is obscured by the 

 opacity of the protoplasm. B, An individual in the act of capturing ita prey 

 (P 1 ), an Infusorian (Urocentrum) ; two pscudopodia have flowed round it, 

 as shown by the arrows, and met at the point c, enclosing the prey ; another 

 Infusorian (P 2 ) is seen in a food vacuole in the body ; N., nucleus ; other 

 letters as in A. After Leidy (226), magnified 200 diameters. 



Further, the body in organisms of the bacterial type is of definite 

 form, limited in many cases by a rigid envelope or cuticle, and 

 special organs of locomotion are either absent or present in the 

 form of so-called " flagella," structures perhaps different in nature 

 from the flagella of truly cellular organisms. But the most remark- 

 able and significant feature of organisms of the bacterial type is 

 seen in the many different modes of metabolism and assimilation 



* The significance of the terms " nucleus," " cytoplasm," " chromidia," etc., 

 w ill be explained more fully in subsequent chapters. 



