PARASITES DUKING THEIB WHOLE LIFE. 267 



to the secret of their astonishing, we may say, their 

 prodigious fecundity. 



Nature requires millions of aphides in a few hours, 

 to arrest the exuberance of vegetation, and as if she 

 distrusted the assistance of the male insect, she dis- 

 penses with it, and the female brings into the world a 

 daughter already prepared to produce a grand-daughter. 

 Generations succeed each other with such rapidity, 

 that if the daughter at her birth were to meet with 

 any obstacle in her passage, the grand-daughter might 

 come into the world before her mother; a single egg 

 can produce in the course of one season milliards of 

 individuals. Each plant has its own aphis, and in many 

 localities the ravages of the Aphis laniger are but too 

 well known, though it was unknown in Europe a 

 quarter of a century ago. 



The Gyrodactylus elegans, of which we have spoken 

 above, contains embryos similarly enclosed, and if these 

 facts had been known at an early period, the celebrated 

 theory of the enclosure of germs, so warmly advocated 

 by Bonnet, would have preserved still longer its intrepid 

 defenders. 



With but few exceptions, all the Hemiptera are para- 

 sites of the vegetable kingdom. There are only very few 

 which attack animals. There is one species, the name 

 of which may be readily guessed (Acanthia lectularia), 

 which pursues us relentlessly everywhere, for it will 

 wait for months and years, always equally greedy of 

 our blood. It surprises us during the night, and does 

 not wait till its digestion is complete before it attacks 

 us again. Happily for us, another hemipterous insect, 

 the masked reduvius (Redtwius personatus) penetrates like 



