50 BIOLOGY OF THE PROTOZOA 



nection with the preparations for sexual activities of the organism, 

 a very general conclusion which, so far as it goes, appears to be 

 justified by the rapidly accumulating facts concerning chondrio- 

 somes in the sex cells of Metazoa. 



5. Chromoplastids and Pyrenoids.— Other permanent cytoplasmic 

 structures of the Protozoa are the color-bearing bodies termed chro- 

 moplastids, chloroplastids or chromatophores, and the pyrenoids, 

 both of which are characteristic of the autotrophic forms, whose 

 nutrition is dependent upon photosynthesis (see Chapter IV). 

 They are found mainly in the group of flagellates although an occa- 

 sional form in other groups of Protozoa may contain them {e. g., 

 Pavlinella chromatophora, CJilamydomyxa montana, amongst rhizo- 

 pods). Pyrenoids usually accompany and are embedded in the 

 chromoplasts. 



Chromatophores vary greatly in form and size; spherical, discoidal, 

 band-form, ring-form, spindle-form and irregular types are known, 

 while the number in a single organism may vary from 1 to 100 or 

 more. They invariably increase by division and are to be regarded 

 as permanent organoids of the cell. Division, however, may in 

 some cases at least be quite independent of the division of nucleus 

 or cell body. The pyrenoids are usually spherical and are char- 

 acteristically refractile structures either single in the cell or as 

 numerous as the chromoplastids. Like the latter they also may 

 reproduce by division. 



The ability to create different colored substances included gen- 

 erally under the heading chromojjhyll is the chief characteristics of 

 chromoplastids. The colors vary from the typical plant green chlo- 

 rophyll, of various shades of green (Phytomonadida?, Chloromasti- 

 gidse), through brown and yellow colors (Chrysomonadidse), blue- 

 green {Paulinella chromatophora), and red (hematochrome). In the 

 majority of forms the coloring matter appears to be identical with 

 the chlorophyll of higher plants; the yellow colors, especially that 

 of the Dinoflagellata, resembles the coloring matter (diatomin) 

 of the diatoms, while the red color, hematochrome, is a modification 

 brought about apparently by the diminution of nitrogen and phos- 

 phorus in the surrounding medium (see Reichenow, 1909). 



Chromatophores are not to be confused with the s\'mbiotic algse 

 which live normally in the protoplasm of many kinds of Protozoa 

 (e. g., "yellow cells" of Radiolaria, Zoochlorellffi of Paramecium 

 hursaria, etc.). In all cases the green chlorophyll is readily trans- 

 formed, as in higher plants, into yellow xanthophyll, and the red 

 hematochrome into green chlorophyll by treatment with dilute 

 alcohol. 



D. Metaplastids of the Protozoa.— In the protoplasm of all 

 Protozoa, in addition to the permanent granules of one kind or 

 another described above, there are many types of transitory or 



