PARASITES. 87 



guest, that sooner or later he may pass into the body of 

 his accustomed Amphitryon. In order thoroughly to 

 know these sedentary or vagabond populations, we 

 must not only study them at the different periods of 

 the year, and under all the conditions of their irregular 

 life, but it is necessary to follow them from the moment 

 that they quit the egg till their complete evolution, 

 closely noticing all that relates to their reproduction. 



In the dung of the cow, by the side of the elegant 

 Pilobolus, live masses of small eels, born in the stomach 

 of the animal, which wind and twist like microscopical 

 serpents, and do not seek the slightest help from the 

 organ which shelters them. They are hatched in the in- 

 terior of the stomach, as if it took place in the meadow. 

 These little eels have evidently only the appearance 

 of parasites, and it may be that they render some 

 service in some of the organs through which they pass. 

 This may also be the case with those which live on the 

 feces of others, or which, lodged in the rectum, watch for 

 the prey which is attracted by the odour. These, espe- 

 cially the latter, are rather messmates than parasites. 

 True parasites are animals entirely dependent on 

 their neighbours, unable to provide for themselves, fed 

 entirely at the expense of others. It is generally sup- 

 posed that paTasites are exceptional beings, requiring a 

 place by themselves in the animal hierarchy, and know- 

 ing nothing of the world except the organ which shelters 

 them. This is an error. There are few animals, how- 

 ever sedentary they may be, which are not wanderers at 

 some period of their lives, and it is not even uncommon 

 to find some which live alternately as noblemen or 

 as beggars. Many of them only deserve to be placed 



