PARASITES FREE DURING THEIR WHOLE LIFE. 115 



articulated animals, which neither the naturalist nor the 

 physician ought to ignore. Some of these increase with 

 frightful rapidity on the skin which harbours them, and 

 their name alone is sufficient to inspire disgust, if not 

 horror : others live like leeches at the expense of dif- 

 ferent animals, but without inhabiting them. There are 

 many of these which follow their host everywhere, and 

 which are dreaded not without just reason. 



Of this kind are gnats, fleas, lice, bugs, and a great 

 many others, among which we ought not to forget the 

 acaridse, nor those singular parasites of bats, which 

 bear no slight resemblance to spiders swimming in the 

 midst of the fur. Volumes might be written concerning 

 the organization and the habits of these parasites. These 

 small creatures inspire the naturalist with no more 

 disgust than the earth-worm of our flower-beds, or the 

 salamanders of marshy places. Each one plays its part 

 according to its conformation, and the most abject in 

 appearance is not always the least useful. 



We will select among these parasites some two-winged 

 insects, among which there are many which suck blood. 

 Those which are generally called flies are divided into 

 two groups, under the name of 

 Nemocera and Brachycera ; many 

 of these live only on blood, and 

 are more terrible than the lion 

 and the tiger; in many coun- 

 tries man can defend himself 

 against those fierce carnivora, Fig. 7.— Antenna of a Gnat, 

 but he is there, completely 

 • powerless and without defence against these insects. 



Among the Nemocera are found the gnats (Culex 



