220 FIRST YEAR SCIENCE 



This will keep the mosquitoes from breeding and prevent 

 the diseases. 



Thus mosquitoes and flies, the summer pests, are not 

 only exceedingly annoying, but are very likely to spread 

 disease. The Texas fever which has caused such great 

 financial losses to the cattlemen of the United States is 

 caused by a protozoan injected into the cattle by the bite 

 of a tick. 



103. Worms. Another class of invertebrates is the 

 worms. One of these, the earthworm, was found in the 



EARTHWORM. 

 A great helper of the farmer. 



study of soilmaking to be very important and should be 

 considered in this place. If an earthworm is examined, it 

 will be seen that the body is made up of segments or 

 rings, and that it moves by successively shortening and 

 elongating its body. Extending through the middle of the 

 body is an alimentary canal consisting of a mouth, gizzard 

 for grinding food, stomach and intestines. 



Near the head is a little nerve center. The whole 

 animal may be regarded as built up by the joining of a 

 number of essentially similar segments. A more -minute 

 examination will show that these segments have been 

 materially modified in some portions of the animal, but 



