RHIZOPODA. 



11 



2. Flagellifeea. — This group receives its name from the flagellmTi whicli cliarac- 

 tcrizes the species belonging to it. 



3. Entosph-erida. — In this group the organisms are provided with an hitra-capsu- 

 lar, spheroidal shell, not traversed by radii, in this respect differing from the Discida. 

 They have no nuclear vesicle. The typical genus is Salioinma, of which there are 

 many forms. Haliomma polyacatitJmm is represented in Fig. 6. 



4. AcANTHOMETRiDA. — The mcmbcrs of this division are characterized particularly 

 by a well-develo])ed radial skeleton, the I'adii meeting in the centre of the capsule. There 

 is no enveloping shell, but lateral processes sometimes project from the spines, as in the 

 beautiful J^iphacantha found by the "Cliallenger" expedition, represented in Fig. 7. 



Xiphacantha, magnified 100 times. 



5. PoLYCYSTiNA. — The Polycystina are by far the most numerous in all fossil 

 deposits of Radiolaria. They are very simple forms with skeleton external, more or 

 less compact or continuous, without a nuclear vesicle. The shell may be a simple 

 sphere, or two or three concentric spheres connected by radii, or with external radial 

 outgrowths extending to a length of several times the diameter of the shell. The 

 most numerous fonns, however, belong to the genera Podocyrtis and Eucyrtidiiim, 

 the former represented in Fig. 8. The beautiful JSucecryphialus (Fig. 5) also belongs 

 to this group. In these forms the shell opens at one end, and growth being mainly 

 in one direction said to be unipolar. 



6. CoLLOzoA. — To this group belong a number of soft, gelatinous forms which are 

 frequently aggregated in colonies, and are therefore designated as compound Radio- 

 laria. The animals may be either single or in families. When single the skeleton con- 

 sists of circumferential spicules, isolated from each other. When compound, there 



