190 



i'llOTOZOA. 



\ 



(fig. 130). A fine peripheral framework of spicules may be added to 

 these. In other cases simple or compound lattice-works, and pierced 

 shells of various external form (like helmets, bird-cages, shells, etc.) 

 are found, and on the periphery of these, spicules and needles, and 

 even external concentric shells of similar shape may be formed, 

 e.g., Polycystina (figs. 131 and 132). 



Up to the present time but little has been made out about the 

 reproduction of these animals. Besides fission (Polycyttaria), the 

 formation of spores has been observed. These are formed from the 

 contents of the central capsule, and, after the bursting of the latter, 

 become free-swimming mastigopods. Radiolaria are inhabitants of 



the sea, and swim at the 

 surface, but are also 

 able to sink to deeper 

 levels. 



Fossil remains of Ra- 

 cliolaria have been made 

 known in great numbers 

 by Ehrenberg, e.g. from 

 the chalky marl and 

 polishing slate found at 

 certain parts of the coast 

 of the Mediterranean 

 (Caltanisetta in Sicily, 

 Zante and u.-Egina in 

 Greece), and in particu- 

 lar from the rocks of 

 Barbados and Nikobar, 

 where the Radiolaria 

 have given rise to widely 

 extended rock formations. Samples of sand also from very con- 

 siderable depths have shown themselves rich in Radiolarian 

 shells. 



I. JliiiJitiJiiria monozoa. Endiolaria which remain solitary. 



1. Fam. Thalassicollidae. Skeleton absent or consisting of single spicules 

 not joined together. Thalassicolla (without skeleton) nuclcata Huxl., Physt-- 

 inatinm MiiUi'ri Schn. 



2. Fam. Polycystinidae. The skeleton consists of a simple or divided latticed 

 shell, the long axis of which is bounded by two poles of different structure. 

 IIdiospli(era. Euci/rtidium galca E. Haeck. 



3. Fam. Acanthometridae. The skeleton consists of several radial spicules 

 which pass through the central capsule and unite in its centre, without forming 



1'iG. 131. JIeliospJ>nra echinoidis (after E. Haeckel). 



