General Morphology of the Protozoa 37 



ness or light and also after irradiation with infrared or visible light. With 

 the effects of temperature controlled, light from the blue end of the 

 spectrum is more effective than that of longer wave lengths (108). The 

 accumulation of a similar red pigment in Haematococcus pluvialis has 

 been attributed to the exhaustion of nitrogenous or other foods. Massive 

 production of this pigment occurs also in young cultures exposed to light 

 in a medium containing acetate; salts of butyric and certain other acids 

 show no such effect (152). In acetate-free medium, intensely red "haemato- 

 cyst" stages are commonly developed in bright sunlight but not in dim 

 light (52). 



Photoreceptors 



A stigma is characteristic of many chlorophyll-bearing flagellates, 

 and occurs also in certain colorless phytoflagellates. The stigma of Eu- 

 glenida is typically a flattened mass of reddish granules embedded in a 

 matrix (Fig. 1. 17, D), whereas a granular organization is not apparent 

 in typical phytomonad and chrysomonad flagellates. The stigma of Volvox 

 and related colonial types is said to contain a concave mass of pigment 

 and a hyaline lens (164). The stigma is usually located near the anterior 

 end of the flagellate, but lies near the middle of the body in some species. 

 The typical position in Euglenida (Fig. 1. 17, D) is near the wall of the 

 reservoir. 



Certain dinoflagellates (Pouchetiidae) possess an ocellus composed of 

 a hyaline lens and a dark mass of pigment (melanosome) partially cover- 

 ing the lens. In certain species the melanosome can be extended over 

 the surface of the lens or contracted toward the base (Fig. 1.17, M). The 

 melanosome may be homogeneous except for a core of red pigment at 

 the base of the lens, or may be merely a loose aggregate of granules as in 

 Protopsis neapolitana (Fig. 1. 17, H). 



CYTOPLASMIC INCLUSIONS 



Cytoplasmic food reserves 



Foods of various kinds are frequently stored in the cytoplasm of 

 Protozoa and, in any one species, the amount and type of reserves may 

 vary with environmental conditions. Starch is the major reserve in young 

 cultures of Polytoma iivella; lipids predominate after 15-30 days (220). 

 In P. iiveUa, and probably in Protozoa generally, less food is stored in 

 rapidly growing than in slowly growing cultures. 



Polysaccharide reserves of phytoflagellates occur as granules or as larger 

 bodies sometimes of characteristic shape and size. Synthesis of these car- 

 bohydrates is not dependent upon chlorophyll and may be expected in 

 both colorless and pigmented species. The supposed presence of colorless 

 "chromatophores" (leucoplasts) in non-pigmented phytoflagellates has 

 been questioned (183). Paramylum (or "paramylon") of Euglenida occurs 



