THE RAY-STREAMERS. 67 



organisms develop in the formation of their skeletons such 

 an amount of various fundamental forms, such geometrical 

 regularity, and such elegant architectm-e. Most of the forms 

 as yet discovei*ed, I have given in the atlas accompanying 

 my Monograph of the Radiol aria. ^ Here I shall only 

 give as an example the picture of one of the simplest 

 forms, the Cyrtidosphcera echinoides of Nice. The skeleton 

 in this case consists only of a simple treUiced ball (s), with 

 short radial spikes (a), which loosely surround the central 

 capsule (c). Out of the mucous covering, enclosing the 

 latter, radiate a great number of delicate little pseudopodia 

 (p), which are partly drawn back underneath the shell, and 

 fused into a lumpy mass of mucus. Between these are 

 scattered a number of yellow cells (I). 



Most Acj^ttaria live only at the bottom of the sea, on stoifes 

 and seaweeds, or creep about in sand and mud by means 

 of their pseudopodia, but most Radiolaria swim on the 

 surface of the sea by means of long pseudopodia extending in 

 all directions. They live together there in immense numbers, 

 but are mostly so small that they have been almost com- 

 pletely overlooked, and have only become accurately known 

 during the last fourteen years. Certain Radiolaria living 

 in communities (Polycyttaria) form gelatinous lumps of some 

 lines in diameter. On the other hand, most of those living 

 isolated (Monocyttaria) are invisible to the naked eye ; but 

 still their petrified shells are found accumulated in sucli 

 masses that in many places they form entire mountains ; for 

 example, the Nicobar Islands in the Indian Ai-chipelago, and 

 the Island of Barbadoes in the Antilles. 



As most readers are probably but little acquainted 

 with the eight classes of the Protista just mentioned, I shall 



