3536 



THE LOWEST ANIMALS 



enveloped. Reproduction commonly takes place by simple division of the animal 

 into two. The common sun animalcule occurs abundantly among the weeds in 

 clear pond water. The green sun animalcule (Acanthocystis) figured above is pro- 

 vided with a skeleton composed of fine siliceous rods or rays, the inner ends of 

 which, buried in the body, are tipped with little discs, the outer ends being either 

 simple or forked. 



In another species the siliceous needles are arranged tangentially; further, the 

 skeleton may be formed of a siliceous latticed sphere, as in the lattice animalcule 

 (Clathrulmd) , which grows fixed to aquatic plants by the base of its long flexible 

 stalk. The body sends its long slender pseudopods through the meshes of the 

 lattice; the total length of the animal is about one-two hundredth of an inch. 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 radiolarians 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 yel- 

 low. They are all marine, and live in 

 zones from the surface to several thou- 

 sand 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 proba- 

 bly 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 espe- 

 cially in surface forms. A few are with- 



LATTICE ANIMALCULE, Clathrulina (magnified 

 350 diameters). 



