RADIOLARIANS. 



56i 



Sun-animalcules often form colonies which result from the buds or the products 

 of division remaining in contact and partly attached. The most likely places to 

 find sun-animalcules are pools in the 

 woods, where the bottom is covered 

 with dead leaves, and among aquatic 

 plants in ponds. 



Order Radiolaria. 



Both alive and in the form of 

 their skeletons many of the radiol- 

 arians are surpassingly beautiful. 

 Floating on the surface of the ocean, 

 their tiny spheres or pyramids of 

 translucent jelly glow with rich tints 

 of crimson, blue, or yellow. They are 

 all marine, and live in zones from the 

 surface to several thousand fathoms. 

 Many of the surface forms avoid a 

 strong light, and only appear after 

 sunset. Certain species which live in 

 depths below one hundred fathoms, 

 and whose bodies contain a dark 

 green or black pigment, are prob- 

 ably phosphorescent Radiolarians 

 are usually known by the flinty 

 skeletons formed by many of them; 

 yet it is not this feature which 

 separates them from the other orders 

 of rhizopods, but the possession of a 

 membranous central capsule in the 

 centre of the body and surrounding the 

 nucleus. The body - substance outside 

 the capsule is highly vacuolated in 



many species, and especially in surface forms. A few are without a skeleton, and 

 consist of small spherical or oval masses of soft gluey protoplasm, with slender 

 radiating pseudopods, and one or several central capsules; the presence of more 

 than one of the latter indicating a colonial form of growth. In a few species 

 the skeleton is formed of a glassy - looking horny substance, termed acanthin, 

 arranged in the form of radiating spines. 



The vast majority of species secrete a siliceous skeleton which assumes an 

 endless variety of forms, such as trellis-work spheres, concentric spheres or boxes 

 joined by radiating spines, helmets, baskets, lanterns, bee-hives, discs, rings, etc. 

 Haeckel has described over four thousand species, and possibly as many more could 

 be added to this number. Radiolaria are divided into two groups ; in the first of 

 these there is either no skeleton or one of silex, while in the second the skeleton 



vol. vi. — 36 



lattice-animalcule, Clathrulina (magnified 

 350 diameters). 



