152 FORAMINIFERA, RADIOLARIA, DIATOMS LESS. 



The Radiolaria form another group of marine animal- 

 cules, the numerous genera of which are, like the Foram- 

 inifera, amongst the most beautiful of microscopic objects. 

 They also (Fig. 33) consist of a mass of protoplasm giving 

 off numerous delicate pseudopods (psd) which usually have 

 a radial direction and sometimes unite to form networks. 

 In the centre of the protoplasmic cell-body one or more 

 nuclei (nu) of unusual size and complex structure are 

 found. 



Int. caps.pr 

 ^- cent caps 



SKcl. 



cqps.fr. 



FIG. 33. Lithocircus annitlans, one of the Radiolaria, showing 

 central capsule (cent, caps.), intra- and extra capsular protoplasm (int. 

 caps.pr., ext. caps. pr. ), nucleus (nit), pseudopods (psd\ silicious skeleton 

 (skel), and symbiotic cells of Zooxanthella (z). (After Biitschli. ) 



In the interior of the protoplasm, surrounding the nucleus, 

 is a sort of shell, called the central capsule (cent, caps.), 

 formed of a membranous material, and perforated by pores 

 which place the inclosed or intra-capsular protoplasm (int. 

 caps, pr.) in communication with the surrounding or extra- 

 capsular protoplasm (ext. caps.pr.). But besides this simple 

 membranous shell there is often developed, mainly in the 

 extra-capsular protoplasm, a skeleton (skel) formed in the 

 majority of cases of pure silica, and often of surpassing 

 beauty and complexity. One very exquisite form is shown 



