XIV COMPLEXITY OF SHELL 153 



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- 

 cystine(B — and should consult the plates of Haeckel's Die 

 Radiolarien . he cannot fail to be struck with the complexity 



Fig. 34. — Skeleton of a Radiolarian (Aclitiomma), consisting of 

 three concentric perforated spheres — the two outer partly broken away 

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

 after Haeckel.) 



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- 

 logy of the group. Imbedded usually in the extra-capsular 



