90 PROTOZOOLOGY 



very diverse pigmentation. In Chloromonadina, the chromatophores 

 are bright green, containing an excess of xanthophyll. In dinoflagel- 

 lates, they are dark yellow or brown, because of the presence of 

 pigments: carotin, phylloxanthin, and peridinin (Kylin, 1927), the 

 last of which is said to give the brown coloration. A few species of 

 Gymnodinium contain blue-green chromatophores for which phyco- 

 cyanin is held to be responsible. The chromatophores of Phytomon- 

 adina and Euglenoidina are free from any pigmentation, and there- 

 fore green. Aside from various pigments associated with the chro- 

 matophores, there are carotinoid pigments which occur often outside 

 the chromatophores, and are collectively known as haematochrome. 

 The haematochrome occurs in Haematococcus pluvialis, Euglena 

 sanguinea, E. rubra, Chlamydomonas, etc. In Haematococcus, it in- 

 creases in volume and in intensity when there is a deficiency in phos- 

 phorus and especially in nitrogen; and when nitrogen and phos- 

 phorus are present sufficiently in the culture medium, the haemato- 

 chrome loses its color completely (Reichenow, 1909; Pringsheim, 

 1914). Steinecke also noticed that the frequent yellow coloration of 

 phytomonads in moorland pools is due to a development of carotin in 

 the chromatophores as a result of deficiency in nitrogen. Johnson 

 (1939) noted that the haematochrome granules of Euglena rubra be- 

 come collected in the central portion instead of being scattered 

 throughout the body when sunlight becomes weaker. Thus this Eu- 

 glena appears green in a weak light and red in a strong light. The 

 chromatophores undergo division at the time when the organism 

 which contains them, divides, and therefore the number of chroma- 

 tophores appears to remain about the same through different genera- 

 tions (Fig. 32). 



In association with the chromatophores are found the pyrenoids 

 (Fig. 32) which are usually embedded in them. The pyrenoid is a 

 viscous structureless mass of protein (Czurda), and may or may not ' 

 be covered by tightly fitting starch-envelope, composed of several 

 pieces or grains which appear to grow by apposition of new material 

 on the external surface. A pyrenoid divides when it reaches a certain 

 size, and also at the time of the division of the organism in which it 

 occurs. As to its function, it is generally agreed that the pyrenoid is 

 concerned with the formation of the starch and allied anabolic prod- 

 ucts of photosynthesis. Pyrenoid (Geitler, 1926). 



Chromatophore-bearing Protozoa usually possess also a stigma 

 (Fig. 32) or eye-spot. The stigma may occur in exceptional cases 

 in colorless forms, as in Khawkinea, Polytomella, etc. It is ordi- 

 narily situated in the anterior region and appears as a reddish or 



