172 ZOOLOGY 



Earthworms are also a source of disease. They burrow into 

 the carcasses of buried animals that have died of infection 

 and bring the disease germs to the surface, where they may 

 infect healthy animals. Thej- are believed to carry the germs 

 of gapes — a worm parasitic in chicks. 



Earthworms belong to the sulj-kingdom of ringed worms 

 (Annelids ^). The annelids are cHvided into two orders, one of 

 which lives chiefly in the sea and is called Pol'ycha?ta,- while 

 the other lives chiefly in fresh water or in the ground and 

 is known as Origochreta. Earthworms belong to the latter 

 order. This order is distinguished, in arldition to its non- 

 marine life, by the alisencc of foot-pads and parapodia, bj^ 

 having few bristles, and by the absence both of tactile append- 

 ages at the head end and of gills. 



The Oligochffta are cither aquatic or terrestrial. The 

 aquatic Oligochceta are among the commonest inhabitants of 

 ponds and ditches, living sometimes in the mud and sometimes 

 at the surface of the water. 



Tubifex ^ is common in slow-running Ijrooks, and lives in the 

 mud of the bottom, forming tubes in it. The thread-like 

 bodies of the worm are stretched up beyond the surface of the 

 mud and wave in the water in graceful undulations. Often 

 the worms are so numerous that their reddish color gives a 

 decided tinge to the bottom. They thrive well in fresh-water 

 aquaria. 



Dero " is very common on the surface of ponds, particularly 

 in the midst of duckweerl (Lemna), the leaves of which it 

 cements together to form a floating tube in which it lives, and 

 by which it is accompanied in all its migrations. Dero can 



^nnnulus, a little ring. s luhus, tube ; faccrc, to make. 



^ poly, many ; chwta, hair, 'dero, to skin or flay. 



