^M THE NEW EVOLUTION ®ll 



RoTiFERA — rotifers or wheel-animalcules . — A large group of uni- 

 versal occurrence in fresh water, but represented by only a few 

 species in the sea. Many of them are able effectively to protect 

 themselves when the pools and ponds dry up, and many can 

 survive heat almost as high as the boiling point. With the dry- 

 ing up of water the encapsuled rotifers and their eggs are blown 

 about and very widely scattered. Because of the great facility 

 with which they are distributed by winds, rotifers are always to 

 be found in water which has collected in sagging gutters, in the 

 axils of epiphytic plants on telephone wires or high up in the 

 trees — in fact anywhere that water collects and stands for a few 

 days. Many kinds of rotifers may be obtained by letting marsh 

 hay or even bark from trees in moist localities soak in water for 

 a week or so. Even bark from logs that have been stored 

 for some time in a cellar will sometimes yield rotifers. They 

 always appear in aquaria, and usually in goldfish bowls. A few 

 rotifers are parasitic, living in the intestines of earthworms, 

 in the canals of fresh water jellyfishes, in the body cavity of 

 sea-cucumbers, on crustaceans, and elsewhere. (Figs. 134, 136, 

 p. ^03.) 



PoLYzoA — moss animalcules . — A large group almost entirely 

 marine, occurring from between tide marks down to the deepest 

 portions of the sea, though most abundantly represented in 

 shallow water and in water of moderate depth. One section of 

 the group, and a few species in another section, live in fresh 

 water. Most polyzoans form moss-like, leaf-like, fan-like, vine- 

 like, or simply encrusting colonies; but a very few species are 

 solitary. The most conspicuous fresh water type forms large 

 jelly-like masses, usually in late summer, about sticks or other 

 supports. In one fresh water type the colony as a whole crawls 

 about like a worm. (Figs. 67, 68, p. iii; 90, p. 175.) 



Vermiformes. — A very large and exceedingly diversified group 

 including the tapeworms, flukes, turbellarians, spiny-headed 

 worms, nematodes or thread-worms, gordian worms or "hair- 

 snakes," and various other types. Most of the species are 

 internal parasites in other animals, a few are external parasites, 

 some live in plants, and some are free living, these last occurring 

 in the sea, in fresh water, and in moist earth. Some are parasitic 

 at one stage and free living at another, and many are parasitic 

 in one type of animal in the young stages and in a wholly different 



