292 THE PROTOZOA 



ties, is definitely established in a number of cases. The materials 

 thus secreted vary in nature from purely inorganic solids, like calcium 

 carbonate, silica, etc., to chitin, cellulose, fats, and jelly-like protoplas- 

 mic products. The simplest cases of secretion are seen in those 

 Mastigophora and Sarcodina where the outer protoplasm becomes 

 gelatinous, to form the jelly-like mantles of different types (many 

 Flagellidia, Heliozoa, Radiolaria). In Amoeba there is a secretion of 

 such a substance which aids the animal in securing food by sticking 

 it to larger objects, as well as by ensnaring the prey (Rhumbler, Ver- 

 worn, Hofer). In Euglena, according to Klebs ('86), the protoplasm 

 throws out a slimy mantle when the surrounding conditions are un- 

 suitable. This mantle at first is not homogeneous, but is in the form 

 of minute gelatinous threads which arise beneath the cuticle from the 

 outer protoplasmic layer of the body. A network is then formed be- 

 tween the threads, which finally unite to form a homogeneous man- 

 tle about the animal. An identical process has been described by 

 Schewiakoff ('94) and by Siedlecki ('99), in the movements of certain 

 gregarines, 1 where a gelatinous layer beneath the membrane secretes 

 filaments of slime-like material which harden outside the body. 



In other instances the secreted material is in the form of granules 

 which unite outside the body to form stalks or houses, or even shells. 

 In many such cases the granules have not been a part of the body 

 protoplasm, although they may have been created there. Such, for 

 example, are the lime shells of the Reticulariida, or the silicious and 

 acanthin skeletons of the Radiolaria. In other cases they appear to 

 be a growth product of the organism, as in the branched stalks of 

 many Flagellidia, although even here foreign particles may be used 

 for this end. Thus, in freshly formed AnthopJiysa stalks, Kent 

 and Butschli observed that the excreted material was granular, and 

 Ehrenberg had already noticed that, if AnthopJiysa colonies are fed 

 with indigo, the colored particles collect at the base of the animal, 

 while Kent ('81), repeating the experiment, observed that the gran- 

 ules were actually deposited to form a part of the new stalk material. 

 The materials for the shells of Rhizopoda may be foreign particles 

 analogous to the indigo granules, or they may be the result of chem- 

 ical activity of the protoplasm. The various shells of Difflugia, Cen- 

 tropyxis, Cyphoderia, LitJiicolla, etc., are examples of the first type, 

 while Euglypha, Qiiadrula, most Heliozoa, Reticulariida, and Radio- 

 laria are examples of the second. 



In the Sarcodina, where the shells, as in Reticulariida, are formed 

 by deposition of calcium carbonate, it has been shown by Carpenter, 

 Kolliker, Wallich, and especially by Dreyer ('92), that the material 



1 Cf. P . 149. 



