AUGUST 169 



hear some of the strangest characteristics of animal 

 existence. I dare not quote more than one example, 

 for fear of shocking tender constitutions, and that shall 

 not be one of which human beings have to dread the 

 attacks, for the creature depends only on the frog and 

 a water-snail as its hosts. It is one of the Nematodes 

 or threadworms (Rhabdonema nigrovenosum), of which 

 the disgusting life-history begins when it is hatched 

 within the body of its mother. The young brood 

 devour her internal organs, and having accomplished 

 her destruction, escape into the water as free creatures. 

 The next change comes when one of these matricides 

 is swallowed by a frog ; it makes its way directly into 

 the lungs, where it grows to be a worm an inch long. 

 Though itself the offspring of two parents, this worm 

 is now a protandrous hermaphrodite, and generates a 

 number of embryos of two distinct sexes. These em- 

 bryos escape through the alimentary canal of the frog, 

 taking up their abode in the excrement, where the sordid 

 cycle begins over again. The peculiarity of all this is, 

 not the alternation of generations that is far from 

 uncommon but that a sexual free-living form should 

 alternate with a hermaphrodite parasitic one. 



