MORPHOLOGY AND PHYSIOLOGY 39 



Chromatophore-bearing forms usually contain also a red- 

 pigmented spherical, ovoid, or elongated body known as the 

 stigma, or eye-spot (Fig. 15), which is a cell-organ that responds 

 to light stimulation. The stigma is composed of an oily sub- 

 stance (lipochrome) and in a number of cases possesses a second- 

 ary structure made of a paramylum body which seemingly func- 

 tions as a lens system. 



Oils and fats are widely distributed among various Protozoa. 

 In some cases they serve not only as reserve food material but 

 also for other purposes. Their function may be hydrostatic, as 

 in Radiolaria, or photogenic, as in various Dinoflagellida. In 

 some cases the oil droplets which are liberated into the water by 

 the disintegration of the protozoan body result in an objection- 

 able odor, as was reported by Calkins in the case of Uroglenopsis 

 americana (Fig. 30). 



Pigments and crystals are also commonly observed in vari- 

 ous Protozoa. These are, as a rule, products of catabolism. Not 

 infrequently a common ciliate such as Paramecium may contain 

 a number of crystals in the endoplasm. According to Schaeffer, 

 these crystals in Amoeba proteus, A. discoides and A. duhia, are 

 characteristic to each species (Fig. 80). In malarial organisms 

 brownish granules, known as melanin pigment, are formed as a 

 result of absorption and digestion by the organisms of the 

 haemoglobin of the erythrocyte. The coloration of Blepharisma 

 lateritia is due to the presence of a specific pigment, as was 

 stated above. 



Certain groups have an endoskeleton. In Trichomonas and 

 allied Mastigophora, there is a conspicuous rod-like structure 

 which makes the axis of the body. It is commonly known as the 

 axostyle and is understood to serve as a supporting and streng- 

 thening cell-organ of the body (Fig. 61). In other forms a num- 

 ber of filamentous structures known as axial filaments may be 

 present to form an endoskeleton (Fig. 63). These structures 

 are especially noted in the Mastigophora which inhabit the di- 

 gestive tract of animals. 



References 



BuLLiNGTON, W. E. 1925 Study of spiral movement in the 

 ciliate Infusoria. Arch. f. Protistenk., Vol. 50. 



