190 Natural History of Entozoa. 



NATURAL HISTORY OF ENTOZOA. 



One of the most astonishing arrangements of Nature is the pro- 

 duction, in enormous quantities, of a class of animals destined 

 to live during a part, or the whole of their existence inside 

 creatures of a higher organization, boring into their structure, 

 imbibing their juices, and often causing their decease. We do 

 not wonder very much that a cat should catch a mouse, a hawk 

 pounce upon a sparrow, or a fox carry off a goose to replenish 

 his larder in the woods. In such cases the carnivorous assailant 

 behaves very much after our own fashion, and an absence of 

 culinary practices marks the chief difference between his mode 

 of conducting the commissariat department and that which 

 pertains to the human kind. Making, now and then, a dainty 

 exception, the larger carnivorous animals munch away at the 

 carcases of their victims till every edible portion has disappeared. 

 Quite different from these magnates of destruction, who devour 

 their fellow- creatures wholesale, is the humbler class of anti- 

 vegetarians, who get their living as parasites, dealing in a 

 small retail fashion, a little bit at a time, with the bodies 

 of larger animals, which they attack from within, or assail from 

 without, according to the precise nature of the food they 

 require, and, the implements of destruction they possess. 

 External parasites belong to various families and orders of 

 animated beings, those best known being furnished by the 

 insect tribes, though others, equally common and interesting, 

 are small cousins of the crabs. Passing to the internal para- 

 sites, we find amongst them representatives of distinct classes. 

 We note, for instance, that many insects lay their eggs in the 

 bodies of other animals, while' the multifarious creatures known 

 as intestinal worms supply the most remarkable instances of 

 eccentric forms, wonderful transformations, amazing migrations, 

 and insidious assassinations of their unfortunate hosts. Our 

 friend, Dr. Oobbold, is remarkably fond of considering the 

 superior animals, man included, in his capacity of " host," or 

 hostelry for parasites of this kind. Although eloquent in 

 warning us against the dangers of allowing ourselves to 

 become a house of call for incipient tape-worms out of place, 

 or for other vagabond entozoa in search of such board and 

 lodging as our livers, muscles, eyes, brains, or intestines may 

 afford, he delights in contemplating the curiosities of their 

 structure, and draws their portraits with such affectionate skill 

 as to make good their pretensions to beauty of a singular, but 

 easily recognizable sort. 



It is convenient to consider the entozoa as one group ; but 

 when we come to study their organization, we find that a 



