26 GUIDE TO THE FOSSIL INVEETEBRATE ANIMALS. 



Class RADIOLARIA. 



X. The central mass of protoplasm with the nucleus is 

 surrounded by a horny membrane, forming a capsule. This, 

 in its simplest form, is spherical, and scattered evenly over 

 its surface are numerous pores through which the protoplasm 

 within it communicates with that outside it. In a higher 

 stage the pores are grouped into several areas, but these in 

 their turn are evenly distributed, so that there is still no 

 definite axis. All these constitute the Porulosa of Haeckel. 



Fig. 6. — Radiolaria, Recent and Fossil, a, a living Radiolarian of the 

 Order Nassellaria, Cyrtocalpis urceolus. Within the siliceous test is 

 seen the central capsule, from the lower part of which the pseudopodia 

 stream out through the mouth and lower meshes of the test. In the 

 upper half is the large nucleus, on each side of which is an oil globule. 

 The lighter round bodies are yellow algse. Enlarged 200 diameters. 

 (After Haeckel, 1887.) h-e are fossil Radiolaria, h, c, and d being of 

 Carboniferous age, and e being Silurian, h and e are examples of 

 Spumellaria Sphaeroidea ; c of Spumellaria Discoidea ; and d of 

 Nasselaria Cyrtoidea. All greatly magnified. (After Riist.) 



In the other Eadiolaria, which Haeckel names Osculosa, the 

 pores are concentrated in a basal region called the osculurn ; 

 thus the capsule has a central axis with a basal and an apical 

 pole ; smaller oscula may occur near the latter. In each of 

 these divisions a skeleton may be developed, either of pure 

 silica or of other substance. 



On these bases the Eadiolaria are divided by Haeckel 

 into four Orders : 1. Spumellaria : Porulosa, with pores 

 scattered; skeleton of solid silica. 2. Acantharia : Poru- 



