PROBLEM I. The Kinds oj An'wials oj the Earth 57 



Oesophagus Crop Gizzard Intestine 



Pharynx 



Mouth Head ganglion Hearts Blood vessels Nerve chain of ganglia 



Fig. 81 Front end of an earthworm cut open. The blood vessels, nerves, and many 

 other parts are similar to those of 7/;ore complex animals. See Figure 82, also. 



Three Phyla of Worms 



PHYLUM - ANNELIDS 



Worjiis with Segments 



Earthworms and their relatives. Perhaps 

 the most important of the Annehds 

 (ann''ell-ids) are the earthworms. You 

 will find them interesting to study. 

 See Exercise 9. Most of the time earth- 

 worms burrow underground where 

 they literally eat their way through the 

 earth, swallowing soil particles and de- 

 caying plant material, which is their 

 food. The food is used and the undi- 

 gested soil is left behind in little ropes 

 which hold together until they are dry. 

 You may have seen them on the ground; 

 they are called castings. Charles Darwin 

 and his sons studied the activities of the 

 earthworm with great care. They dis- 

 covered that the animal often brought 

 its castings to the surface and that, 

 therefore, on a small scale, earthworms 

 were constantly plowing and cultivating 

 the soil, making themselves useful to 

 man. If you look at Figure 81, you will 

 see that the body is made up of rings 

 or segments. All the M^orms in this 

 phylum are segmented. One fresh water 



form that is rather common is the 

 leech. There are suckers at both ends 

 of the body which enable it to stick 

 tightly to the animal from which it 

 sucks blood; that is the origin of the 

 expression, "sticks like a leech." It has 

 teeth with which it breaks through the 

 skin and a substance in the saliva which 

 prevents the clotting of blood; thus it 

 can suck until it is full. 



PHYLUM - NEMATHELMINTHS 



Roimdworms 



The hookworm and its relatives. There 

 are other Nemathelminths (nem-a- 

 thel'minths) but the hookworm is the 

 best known of this group. In later 

 chapters you will read more about them. 

 Hookworms and some other members of 

 this phylum live in the bodies of both 

 man and other animals where they may 

 cause disease. Most of the roundworms 

 are tiny, too small to be seen w ith the 

 naked eye. Their bodies have no seg- 

 ments. Thev are present in large num- 

 bers everywhere, particularly in the soil, 



