MORPHOLOGY 



39 



material for the construction of their shells. According to Cush- 

 man, Psammos'phaera fusca uses sand-grains of uniform color 

 but of different sizes, while P. parva uses grains of more or less 

 uniform size but adds, as a rule, a single large acerose sponge 

 spicule which is built into the test and which extends out both 

 ways considerably. Cushman thinks that this is not accidental, 

 since the specimens without the spicules are few and those with a 

 short or broken spicules are not found. P. howmanni, on the other 

 hand, uses only mica flakes which are found in a comparatively 

 small amount, and P. rustica uses acerose sponge spicules for the 



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

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



framework of the shell, skillfully fitting smaller broken pieces into 

 polygonal areas. Other foraminiferans combine chitinous secre- 

 tion with calcium carbonate and produce beautifully complicated 

 shells (Fig. 4) with one or numerous pores. In the Coccolithidae, 

 variously shaped platelets of calcium carbonate ornament the 

 shell. 



The silica is present further in the shells of various Protozoa. 

 In Euglypha and related testaceans, siliceous scales or platelets 

 are produced in the endoplasm and compose a new shell at the 

 time of fission or of encystment together with the chitinous secre- 

 tion. In many heliozoans, siliceous substance forms spicules, 

 platelets, or combination of both which are embedded in the 

 mucilaginous envelope which surrounds the body and, in some 



