DERIVED ORGANIZATION— TAXONOMIC STRUCTURES 137 



of chemical stimuli, was able to demonstrate a voluminous gelatinous 

 envelope secreted by Colpidium campylum. Similar secretions were 

 also demonstrated in other filiates and in certain rhizopods and 

 flagellates as well. The secreted material, which he called "tektin," 

 appears to be a combination of an albumin complex and a carbo- 

 hydrate complex and, according to Bresslau (see also Schneider, 

 1930) it is instrumental in forming shells and tests of Protozoa, as 

 well as trichocysts of many types. 



The most characteristic shell-forming material manufactured by 

 Protozoa is chitin and pseudochitin. Chemically chitin is a modified 

 protein (C30H50O10N4 or multiple) and is undoubtedly polymorphic 

 in composition. Its mode of formation is still unproved, but condi- 

 tions in Protozoa support the view of Chatin that it arises by trans- 

 formation or differentiation of the peripheral cellular protoplasm. 

 Not only are cups, tests, "houses" of various kinds formed of 

 these substances, but cyst membranes, spore capsules of the Sporo- 

 zoa and "central capsules" of the Radiolaria as well, while impreg- 

 nated with calcium carbonate, silica, strontium sulphate, etc., or 

 covered by foreign bodies of different kinds, the chitinoid mem- 

 branes furnish the framework for the up-building of the most 

 complex shells and skeletons. In encysting ciliates the animal 

 becomes spherical, much condensed by loss of water and is sur- 

 rounded by an envelope of fluid-like material which condenses more 

 and more with exposure until the definite membrane, impervious 

 to moisture and resistant to all unfavorable conditions of the 

 environment, results. In Radiolaria the central capsule is a spherical 

 wall of chitin, separating the endoplasm from the external proto- 

 plasm and perforated in various ways to permit of communication 

 between the different regions of the cell (see p. 439). 



In flagellates and ciliates the chitinous houses, tests, cups, etc., 

 are usually colorless and very transparent, but in the rhizopods this 

 is unusual, the chitin shells being colored by oxides of iron usually 

 red or brown (Arcella sp., etc.). In the majority of fresh water 

 rhizopods the outer surface of the chitinoid shell is covered by foreign 

 particles of various kinds, such as sand crystals, diatom shells, or 

 even living algae, which are glued to the membranes by a chitinous 

 cement. Similar shells, which are generally known as arenaceous 

 shells, are found amongst the Foraminifera. In other cases, plates 

 of silica are deposited in the inner protoplasm and passed out during 

 reproduction to be cemented on the chitinous membrane in regular 

 patterns (Euglypha aheolata, Fig. 9, p. 31). Foreign bodies caught 

 up in the wrinkles of withdrawing pseudopodia are similarly stored 

 in the protoplasm to be used for shell-building purposes, Verworn, 

 for example, compelling Bifflugia to build its shell of differently 

 colored powdered glass. 



