FLAGELLATE AND CILIATE PROTOZOA 



241 



forms containing chroma tophores. The red " eye-spot" is usually 

 located at the anterior end of the body near the base of the flagellum 

 and probably functions as a sense organ, being stimulated by rays 

 of light. Chromatophores, oil droplets, and pigment spots may 

 sometimes be found in Infusoria but are much less common than 

 among the flagellates. 



Generally speaking, the physiological processes in Mastigophora 

 and Infusoria are carried on precisely as in Sarcodina. The pres- 

 ence of chlorophyl in some of the flagellates makes possible the 

 synthesis of food from inorganic elements, but in many of these 

 forms and in nearly all of the ciliates distinct mouths are developed, 

 sometimes permanently open and sometimes open only while food 

 is being ingested. The symbiotic relationship exists with algae 

 in some species of ciliates also. Among Mastigophora food is 

 often whipped down by the flagellum to the soft ectoplasm at its 

 base where ingestion takes place. The delicate collars present in 

 some flagellates assist in food getting. Among ciliates the vibrat- 

 ing cilia, membranelles, and membranes serve to draw food toward 

 the animal by arousing currents of water. In Suctoria the tentacles 

 are organs for securing food, their distal extremities being provided 

 with openings through which the protoplasm of the prey is drawn. 

 Respiration and excretion are similar processes in all Protozoa. 

 The contractile vacuoles assist in the excretion of waste fluids and 

 probably of gases. In some Infusoria there are definite points on 

 the surface where waste solids pass from the body. 



Among the Mastigophora, longitudinal fission is the predominating 

 method of reproduction, only a few forms dividing transversely. 

 Usually the chroma tophores, "eye-spot" and pyrenoids, if present, 

 divide as well as the nucleus during reproduction. The flagellum 

 sometimes divides longitudinally, and in other forms is cast off, 

 new flagella being developed as the cells separate. In some cases 

 the "eye-spot," pyrenoids, and flagella are duplicated before a 

 division of the cell commences. Many colonial forms of Masti- 

 gophora illustrate a highly specialized type of cell division similar 

 to that shown in a metazoan ovum. Among Infusoria simple 

 division is the predominating method of reproduction. Division 

 may be longitudinal, transverse, or diagonal, both nuclei dividing 



