RADIOLARIANS. 
RADIOLARIANS. 561 
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 
lattice-animalcule, Clathrulina (magnified 
350 diameters). 
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 
