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. 



Stel. 



Int. caps, pr 

 cent caps 



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

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

 caps, pi'., ext.caps.pr.}, nucleus (nu), pseudopods (psd}, silicious skeleton, 

 (skel}, and symbiotic cells of Zooxanthella (2). (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 (/;//. 

 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 



