42 ANIMALS or LAND AND SEA 



man. Some have very painful bites, and some have been shown 

 to transmit dangerous diseases. The mites are mostly small 

 and many are almost invisible. Some are vegetarian or feed 

 on decaying matter, while others are predaceous and many are 

 parasitic. The most familiar are the "red-bugs," ''jiggers" 

 or "betes-rouges," so very annoying in the spring time in the 

 south, and the itch-mites of various sorts. There are very 

 many kinds of mites which attack man, even among plant- 

 feeding types. One mite has been proved to transmit disease. 

 Related to the mites but much larger are the curious tongue- 

 worms which hve in the lungs and air passages of carnivorous 

 mammals and reptiles and when young are internal parasites. 

 Both the adults and larvae are sometimes found in man; these 

 usually are of a species from the dog, though they sometimes 

 come from snakes. 



Of the leeches the most important as human parasites are 

 the land-leeches which are a miserable pest in many warm 

 moist countries, and those small leeches which, taken in with 

 water in the act of drinking, attach themselves to the lining of 

 the mouth and nasal passages. 



There are three types of so-called "worms" which habitually 

 feed upon the human body or live on the results of its activities. 

 The flat-worms or flukes are most remarkable creatures with a 

 life history so complicated it is a marvel that any at all survive. 

 In many cases the chances are more than a million to one 

 against any single egg developing to maturity; and yet there 

 are plenty of these creatures. The life history of one of the 

 flukes has already been given in the introduction; in some the 

 hfe history is still more complicated, involving three entirely 

 different hosts. All of the flukes infesting man, over twenty 

 kinds of blood flukes, liver flukes, lung flukes and intestinal 

 flukes, are parasitic in fresh water snails at some stage of their 

 development. 



Everyone has heard of tapeworms. These are related to 

 the flukes. They have a somewhat less complicated life his- 

 tory, though most of them live in one host in the earlier, and 



