GENERAL SKETCH 



37 



some species in which colored masses of protoplasm '■ — chromatophores 

 — are present, either as living parts of the cell (Mastigophora) or as 

 commensals or symbionts, the protozoon and the plant living together 

 for mutual benefit (Infusoria, Sarcodina). The chromatophores are 

 colored by different substances, usually green by chlorophyl (Chloro- 

 monadina, some Infusoria), or brown by diatomin (Chrysomonadidse 

 and Dinoflagellidia), and have a definite shape and size for each 

 species. Brilliantly colored patches of pigment, the so-called eye- 

 spots or stigmata, are frequently seen, chiefly among the Mastigoph- 



A B 



Fig. II. — Flagellates with stigmata. [FRANCE.] 

 A, Euglcna Ehrenbergii, Klebs. The color-mass (s) contains several concrements (lenses ?) . 

 B, Pandorma morum, Ehr. The color-mass (s) is attached to a single spherical lens. 



ora, where they are situated near the base of the flagellum. These 

 spots are supposed to have some special relation to light, 1 an unproved, 

 though probable, view which is based chiefly upon the fact that in 

 many of them there is a distinct lens-like body, and other structures 

 which usually accompany eyes of primitive form in other types of 

 invertebrates 2 (Fig. n). 



Among other inclusions occasionally found within the endoplasm 

 are the peculiar trichocysts found in the holotrichous ciliates (Para- 

 mecium and its allies). These are minute defensive or possibly 

 offensive weapons analogous to the stinging threads of the Ccelen- 

 terata. Nematocysts containing a spirally wound thread, as in the 

 Coelenterata, are also found in two forms, one a dinoflagellate (Poly- 

 krikos), the other a ciliate (Epistylis umbellaria),. while analogous 

 thread-bearing structures are found in the spores of all Myxospo- 

 ridiida among the Sporozoa (Fig. 12, C, £>). 



1 Cf. Pouchet, '86. 



2 Engelmann's ('82) experiments, on the other hand, tend to show that it is not the 

 colored body, but the colorless protoplasmic mass in front of the stigma which is particularly 

 sensitive to light. 



