HELIOZOA. 



Greek, hclios, the sun ; coon, animal. 



While the Lobose and Filose Protoplasts ai*e essentially creeping ani- 

 mals, and in all the shell-covered forms habitually move about with the 

 mouth of the shell downward, and with the pseudopods spreading therefrom 

 in contact with the surface on which they move, the Heliozoans or Sun- 

 animalcules are swimmers. Their body is commonly of spherical form, and 

 delicate pseudopodal filaments radiate from every part of its surface. While 

 some are naked or entirely soft, others are provided with a sort of protective 

 skeleton, consisting of radiant spines, of minute spicules imbedded in an 

 exterior protoplasmic layer, or of a delicate latticed shell. 



The soft spheroidal protoplasmic body, in general, exhibits the same 

 essential constitution as in the Protoplasts, and commonly presents but 

 little more distinction of ectosarc and endosarc than in the Filosa. A large 

 proportion of clear globules or vacuoles form a common constituent, giving 

 to the body a foamy appearance, not usual in any of the Protoplasts. 



Generally, the body contains a single central nucleus; but, in a few 

 forms, a number of nuclei occur scattered through the mass. 



In some of the Heliozoans, one or more conspicuous contractile vesi- 

 cles appear on the surface of the body, and exhibit the usual phenomena as 

 indicated in the description of the Protoplasts. As the contractile vesicles 

 enlarge, they rise prominently above the surface of the body, and appear 

 like floating bubbles. In their abrupt collapse and discharge of the con- 

 tents, they often give rise to a visible shock to the body of the animal. In 

 other Heliozoans, if contractile vesicles occur, they have escaped detection. 



Some Heliozoans appear bright green from the presence of chlorophyl 

 in variable proportion, as one of the constituents of the body. 



The pseudopodal rays are in the form of delicate threads of granular 

 protoplasm, emanating from all parts of the body. They are commonly 

 simple filaments, rising by a broad base, rapidly tapering to extreme fineness 

 and variable length, often exceeding the diameter of the body. They 



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