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 (riu) of unusual size and complex structure are 

 found. 



Skel. 



::;i^Inl. caps.jor 

 cent caps 



cqps.jjr. 



Fig. 33. — Lilhocircus annularis, one of the Radiolaria, showing 

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

 caps. pr. , ext. caps, pi: ), nucleus (««), 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 {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 



