476 BIOLOGY OF THE PROTOZOA 



elements forming the basket are much larger than trichites and 

 are frequently combined in such a manner as to justify the term 

 basket. The rods are usually constant in number in a species and 

 may be united to form a tube at the posterior end of the basket 

 or in some cases may be united throughout. In Chilodon the 

 basket is protrusible and serves a useful purpose in food-getting. 

 According to MacDougall (1925) the basket is dissolved in artificial 

 gastric juice (pepsin) indicating a protein composition. 



Metaplastic substances frequently appear in the form of pigments 

 which impart a characteristic color to a species. These are probably 

 connected with food metabolism and disappear in the absence of 

 appropriate food materials. Thus the bine pigment "stentorin'' 

 of Stentor coeruleus, or Folliculina or the lavender of Blepharisma 

 undulans, the red of Mesodinium rubrum, the black spot of Tillina 

 magna, etc., are coloring matters of this type. Fats and oils also 

 are frequent inclusions and when brilliantly colored, as mNassula 

 aurea, give a striking and a pleasing picture as the organism rolls 

 through the water. 



Symbionts are of frequent occurrence and give to Paramecium 

 bursaria, Stentor viridis, Ophrydium versatile and some Vorticella 

 species a bright green color. 



Contractile vacuoles are practically universal among ciliates 

 and Suctoria. Held in place in the denser cortex they never move 

 about with cyclosis. They empty to the outside through a covered 

 but thinned orifice in the cortex, the covering being liquefied at 

 systole (Taylor, 1923). The vacuole system often includes canals 

 and reservoirs, reaching a high degree of specialization in some 

 forms, and ciliated excretory canals are said to be present in a few 

 parasitic types (Pycnothrix, Schubotz, 190S). 



The Infusoria are unique in having an almost universal nuclear 

 apparatus in the form of dimorphic nuclei, macronucleus and micro- 

 nucleus. Of these the macronucleus is large and usually homo- 

 geneous in structure (granular) and is highly variable in shape in 

 different species. In some forms it is multiple and formed by 

 repeated division of an original single nucleus (Uroleptus); in other 

 cases attempted division results in a chain of nuclei connected by 

 a common nuclear membrane, giving rise to "beaded" nuclei 

 (Stentor, Spirostomum ambiguum, Uronychia transfuga, etc.). It 

 is frequently rod-shape as in Diplodinium (Fig. 2, p. 20), or horse- 

 shoe shape as in Vorticella, or very much branched as in Dendrosoma, 

 Ephelota and other Suctoria (Fig. 196). 



Micronuclei are minute and are usually partially embedded in the 

 substance of the macronucleus. There is but little variation in 

 form of the micronucleus in different species, but there is a great 

 variation in the number present. In Paramecium caudatum and 

 P. bursaria there is but one, while in P. aurelia and P. calkinsi 



