124 ANIMAL PARASITES AND MESSMATES. 



in 1666. According to some entomologists, it was in- 

 troduced into Europe in some wood 

 that came from America. It is only 

 necessary to make this slight refer- 

 ence to the Cimices ; their congeners 

 are, for the most part, parasites of 

 plants, and live on their sap. 



To the same order belongs the 

 singular hemipterous insect of our 

 ^^* ' ^ " "^' ponds, the boat-fly {Notonecta). It 



h^s some feet suited for swimming, and others for run- 

 ning, and it swims on its back with great rapidity. It 

 is a dangerous neighbour for everything that has life. 

 Always greedy of blood, it attacks great as well little 

 animals, and sucks the blood of its victim to the last 

 drop, so that it must be closely watched when placed in 

 an aquarium. 



Lice, concerning which we are about to add a few 

 words, are also free parasites, and belong to a different 

 order of insects. Their mouth is formed of a sucker 

 contained in a sheath, without articulations ; it is 

 armed at the point with retractile hooks, within which 

 are four bristles. They have climbing feet, terminated 

 by pincers, with which they seize the hair of the animals 

 on which they live ; their eggs are known by the name 

 of nits. We have represented in Figs. 17, 18, and 19, 

 the complete insect, the head, the sucker, and a claw 

 more highly magnified. 



Lice are hatched at the end of five or six days, and 

 reproduce at the end of eighteen days. Leeuwenhoek 

 calculated that two females might become the grand- 

 mothers of 10,000 lice in eight weeks. They are all 



