22 



BIOLOGY OF THE PROTOZOA 



specific physiological activity in Metazoa seems to be inappropriate, 

 and as Whitman argued, inadequate. 



Cell aggregates or colonies are likewise highly variable in their 

 functional specialization. While many of them consist of fortuitous 

 groups of cells with dimensions A'arying with the number of indi- 

 viduals joined together (e. g., Ophrydium versatile, Dinobryon 

 sertularia, etc.), others are definite in form, number of cells, and in 

 arrangement (e. g., Platydorina caudata, Kof.). Here the colony as 

 such has a distinct individuality and in some cases {e. g., Gonium 

 yectorale) undergoes a definite developmental cycle (Fig. 3). Again 

 some colonies composed of otherwise independent cells do not react 

 as separate individuals but the colony reacts as a coordinated whole. 

 Thus Zudthamnium arhuscida, composed of many hundreds of indi- 



FiG. 4. — Types of Protozoa. A, Amoeba proteus, a rhizopod; B, Peranema tricho- 

 phora, a flagellate; C, Stylonychia mytilis, a filiate; D, a polycystic! gregarine; E, 

 Tokophrya quadri partita, a suctorian. {A, after Calkins, B, C, E, after Butschli; 

 D, after Wasielewsky.) 



vidual cells in a colony which may attain a diameter of 1 inch, 

 reacts as a unit organism if any one of the component cells is irri- 

 tated (Fig. 210) . The entire aggregate contracts into a small ball, so 

 minute that it is scarcely visible. The concerted action is due to 

 the contraction of stalk myonemes which are continuous through- 

 out the entire aggregate, like the coenosarc of some hydroid colonies. 

 For such colonies of j^rotozoa, as for analogous colonies of hydroids, 

 the expression "individual of a second order" has been applied. 



Between the limit's of the simplest and the most complex of uni- 

 cellular organisms are the great majority of the (estimated) 15,000 

 or more known Protozoa. In each of the main subtli\'isions sim- 

 plicity as well as extreme complexity of organization is represented, 

 each subdivision including a series of representati\'e forms ranging 

 from one extreme to the other. Differentiations in the different 



