xiv COMPLEXITY OF SHELL 153 



beauty and complexity. One very exquisite form is shown 

 in Fig. 34 : it consists of three perforated concentric spheres 

 connected by radiating spicules : the material of which it is 

 composed resembles the clearest glass. 



The student should examine mounted slides of the silicious 

 shells of these organisms sold under the name of Poly- 

 cystinea and should consult the plates of Haeckel's Die 



FIG. 34. Skeleton of a Radiolarian (Actinomma), consisting of 

 three concentric perforated spheres the two outer partly broken away 

 to show the inner connected by radiating spicules. (From Gegenbaur 

 after Haeckel. ) 



Radiolarien : he cannot fail to be struck with the complexity 

 and variety attained by the skeletons of organisms which are 

 themselves little more complex than Amoebae. 



Before leaving the Radiolaria, we must touch upon a 

 matter of considerable interest connected with the physio- 



