48 PROTOZOOLOGY 



encystment together with the chitinous secretion. In many helio- 

 zoans, siliceous substance forms spicules, platelets, or combination 

 of both which are embedded in the mucilaginous envelope that 

 surrounds the body and, in some cases, a special clathrate shell com- 

 posed of silica, is to be found. In some Radiolaria, isolated siliceous 

 spicules occur as in Heliozoa, while in others the lateral development 



Fig. 4. Diagram of the shell of Peneroplis pertusus, X about 35 

 (Carpenter), ep, external pore; s, septum; sc, stolon canal. 



of the spines results in production of highly complex and the most 

 beautiful shells with various ornamentations or incorporation of 

 foreign materials. Many pelagic radiolarians possess numerous con- 

 spicuous radiating spines in connection with the skeleton, which ap- 

 parently aid the organisms in maintaining their existence in the open 

 sea. 



Certain Protomonadina possess a funnel-like collar in the flagel- 

 lated end and in some in addition a chitinous lorica surrounds the 

 body. The lorica found in the Ciliophora is mostly composed of 

 chitinous substance alone, especially in Peritricha, although others 

 produce a house made up of gelatinous secretion containing foreign 

 materials as in Stentor (p. 806). In the Tintinnidae, the loricae 

 are either solely chitinous in numerous marine forms not mentioned 

 in the present work or composed of sand-grains or coccoliths ce- 

 mented together by chitinous secretion, which are found in fresh- 

 water forms. 



