DERIVED ORGANIZATION— TAXONOMIC STRUCTURES 133 



in ways that would be impossible for the endoplasm. In simple 

 cases as, for example, in Amoeba proteus, it is not strikingly differ- 

 ent from the endoplasm, but in other cases it becomes a complex of 

 special adaptations and the seat of many important organoids of 

 the cell. The external zone of protoplasm thus becomes practically 

 an organ system with structures and functions quite different from 

 the inner protoplasm. In view of these distinctive features it is 

 frequently called the cortex. 



I. DERIVED STRUCTURES OF THE ENDOPLASM. 

 METAPLASTIDS. 



In the protoplasm of all Protozoa, in addition to the permanent 

 granules of one kind or another described in the preceding chapter, 

 there are many types of transitory or fixed products of cell activity 

 collectively known as metaplasmic granules or metaplastids. All 

 of these are formed during the vital activities of metabolism some 

 of them as reserve stores of food substance formed as products of 

 the building up or anabolic processes of metabolism, others by the 

 destructive or catabolic processes. In the former group are included 

 fats, glycogen, paraglycogen, oils, albumin spheres, etc. In the 

 latter group, as products of destructive metabolism, are included a 

 great variety of crystals, pigment granules, chitin and pseudo- 

 chitin, and other more or less widely distributed products. These 

 products of destructive metabolic activities are frequently so abun- 

 dant as to give the protoplasm a densely granular appearance. 



The form and appearance of these various products of proto- 

 plasmic activities vary within wide limits and will be discussed more 

 fully in connection with the different classes of Protozoa. Many 

 of them serve a useful purpose as reserves in nutrition and other 

 physiological processes, while a number of them are used for pur- 

 poses of support, protection, or shell and skeleton building. Gly- 

 cogen-like bodies are found in a few types of flagellates; true glycogen 

 occurring in the protoplasm of Pelomyxa palustris according to 

 Stole (1900), and in the ciliates Paramecium, Opalina, Glaucoma and 

 Vorticella according to Barfurth. Paraglycogen, also called zooamy- 

 lum, which differs from glycogen in its solubility and in its color 

 reactions when subjected to sulphuric acid and iodine, is present in 

 many ciliates and flagellates as well as in some gregarines. 



Oils and fats are widely distributed. Great oil globules are par- 

 ticularly characteristics of the Radiolaria where, in addition to 

 serving a useful purpose as reserves of nutriment, they also serve 

 a hydrostatic function in the activities of different organisms. 

 Globules of smaller size but conspicuous by their frequently brilliant 

 coloring are found in many types of flagellates and ciliates. 



Protein derivatives in the form of chitin and pseudochitin are 



