THE RAY-STREAMERS. 65 
Kichhornii. To the naked eye it appears as a gelatinous 
grey 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 central 
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, really 
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 Basket-shells (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 are essentially distinguished 
from 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 fine 
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- 
Jaria 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 flinty 
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 bails. In othev 
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