SPECIAL MORPHOLOGY AND TAXONOMY OF INFUSORIA 367 



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 blue pigment "stentorin" 

 of Stentor coendevs, or Follicvlinfi 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 in Nassida 

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

 through the water. 



Chromatophores, as differentiations of ciliate protoplasm are not 

 generally credited although Engelmann maintained that chloro- 

 phyll (?) occurs in Vorticella campanidata. S^'mbionts, however, 

 are of frequent occurrence and give to Paramecmm hursaria, Stentor 

 viridis, Ophrydium versatile and some Vorticella species a bright 

 green color. 



Contractile vacuoles are practically universal amongst ciliates 

 and Suctoria. Held in place in the denser cortex they ne^'er move 

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

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

 at systole (Taylor, 1923). The vacuole system 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 para- 

 sitic t;>T)es (Pycnothrix, Schubotz, 1908). 



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 usualh^ 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 iUroleptiis mobilis); 

 in other cases attempted division results in a chain of nuclei con- 

 nected by a common nuclear membrane giving rise to "beaded" 

 nuclei (Stentor, Spirostomum ambiguinn, Uronychia iransfuga, 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. 159). 



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 difi'erent species, but there is a great 

 variation in the niunber present. In Paramecium, caudatum and 

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

 there are two, and two are characteristic of the Pleurotrichidse. 

 The number of micronuclei runs up to eighty or ninety in Stentor 

 and the number is intermediate in several other genera. 



