THE RAY-STREAMERS. 65 



EicMiornii. To the naked eye it appears as a gelatinous 

 gTey globule of mucus, about the size of a pin's head. 

 Looking at it through the microscope, we see hundreds or 

 thousands of fine mucous threads radiating from the centi'al 

 plasma body, and perceive that the inner layer of its cell- 

 substance is different from the outer layer, which forms a 

 bladder-like membrane. In consequence of its structure, this, 

 the little sun-animalcule, although wanting a shell, reall}^ 

 rises above the structureless Acyttaria, and forms the 

 transition from these to the Radiolaria. The genus Cysto- 

 phrys is of a nature akin to it. 



The BasJict-sJiells (Radiolaria) form the third and last 

 class of the Rhizopoda. Their lower forms are closely allied 

 to the Heliozoa and Acyttaria, whereas their higher forms 

 rise far above them. They a.re essentially disting-uished 

 fix)m both by the fact that the central part of their body is 

 composed of many cells, and surrounded by a solid mem- 

 brane. This closed "central capsule," generally of a glo- 

 bular shape, is covered by a mucous layer of plasma, out of 

 which there radiate on all sides thousands of exceedingly fiiae 

 threads, the branching and confluent so-called pseudopodia. 

 Between these are scattered numerous yellow cells of un- 

 known function, containing grains of starch. Most Radio- 

 laria are characterized by a highly developed skeleton, 

 which consists of flint, and displays a wonderful richness of 

 the neatest and most curious forms. Sometimes this flmty 

 skeleton forms a simple trellice-work ball (Fig. 16 s), some- 

 times a marvellous system of several concentric trelliced balls, 

 encased in one another, and connected by radial staves. In 

 most cases delicate spikes, which are frequently branched 

 like a tree, radiate from the surface of the balls. In other 



VOL. II. F 



