76 



ANIMAL STUDIES 



gether by elastic bands. A sac, the cocoon, is thus pro- 

 duced, containing the eggs and a milky, nutritive substance. 

 In a few weeks the worm 

 develops and, bursting the 

 wall of its prison, makes its 

 escape. 



71. Distribution. The 

 earthworms and their allies 

 are found widely distributed 

 throughout the world, and 

 all exhibit many of the 

 characters just described. 

 The greatest differences 

 arise in their mode of life : 

 some are truly earthworms, 

 but others are fitted for a 

 purely aquatic existence in 

 fresh water or along the 

 seacoast ; a few have taken 

 up abodes in various ani- 

 mals and plants, and in 

 some of these situations they 

 extend far up the sides of 

 the higher mountains. In 

 all, the head is relatively 

 indistinct, the number of 



bristles On each Segment FlG - 42 - A marine worm (Nereis). A, ap- 



few, and for this and other Tote'tim""* 6Ca n ' ^ B ' 



reasons all are included in 



the subclass Oligochaeta, or " few-bristle " worms. 



72. Nereis and its allies. In many of the above-men- 

 tioned situations members of a more extensive group of 

 worms are found, with highly developed heads and many 

 bristles arranged along the sides of the body. These are 

 the Polychaetes or " many-bristle " worms, and as a repre- 

 sentative we may take Nereis (Fig. 42), a very common 



