THE MASTIGOPHORA 171 



is formed by the euglenoid cell, and the othe? constituents of 

 protoplasm must be synthesized when euglenas grow and multiply. 

 In this manner the euglena carries on the holophytic nutrition 

 characteristic of all living bodies that possess chlorophyll. 



But the euglena is further interesting because this is not its sole 

 mode of nutrition. Small organisms, such as bacteria, may be 

 ingested through the gullet (Fig. 91E-G) surrounded by vacuoles, 

 and digested in the cj^oplasm as in the feeding of an amoeba or of 

 other holozoic protozoa. Respiration, comparable with internal 

 respiration in the cells of higher animals, as well as excretion of 

 carbon dioxide, can be shown to occur. 



A third type of nutrition, according to zoological terminology, 

 is known as saprophytic. In this case the organism is unable to 

 synthesize its food from such simple compounds as do the chloro- 

 phyll-bearing organisms. It must depend upon the decomposition 

 products of other plants and animals, after the manner of the 

 moulds and many bacteria that grow upon organic material. 

 When certain species of euglenas are kept in a low illumination 

 and in a medium rich in decomposing organic matter, they lose 

 most of their chlorophyll; and, since they grow and multiply 

 without other nutritive activities, it may be presumed that they 

 carry on their nutritive processes saproph^-tically. Such is known 

 to be the case with many other Mastigophora. 



Reproduction and Life Cycle. — As an example of the condi- 

 tions in one of the common euglenoids, the life cycle of Euglena 

 gracilis may be described. This species is well suited for pur- 

 poses of illustration, because its cycle includes an unusual range of 

 possibihties (Fig. 93). As with the majority of fresh-water pro- 

 tozoa, there is an alternation of " active " and " encysted " phases. 

 In the active phase, the euglenas usually multiply by longitudinal 

 division of the cell, but transverse division may also occur. In the 

 former case (Fig. 93, 2), the pigment spot, the reservoir, and the 

 enlargement at the base of the flagellum divide, to form these 

 parts for the two daughter cells, while the division of the nucleus 

 is in progress. The external part of the old flagellum is always 

 cast off before division begins, and a new one formed by each 

 daughter cell as division proceeds. As these internal changes 

 advance, a division of the cytosome begins at the anterior end 

 and proceeds posteriorly until separation is accomphshed. The 

 nucleus divides by a pecuhar type of mitosis (cf. p. 137). In 



