GREAT STEPS IN EVOLUTION 103 



worms without number. A vivid impres- 

 sion of the prevalence of parasitism is afforded 

 by the capture, not infrequent at a chan- 

 nel zoological station or by fisher folk any- 

 where, of the huge and majestic sunfish, 

 Orthagoriscus mola; and by picking off with 

 forceps into museum bottles his crowds of 

 uninvited passengers the tuft of barnacles 

 upon his back, the biting isopods like enor- 

 mous fleas upon his skin, the trematodes 

 sucking like leeches upon his eyes; and within 

 to find not only his alimentary canal 

 crammed with worms more than with food, 

 and his liver changed from its natural brown 

 almost into the likeness of a tangle of white 

 worsted, of which each thread is a tape- 

 worm. Neither frog nor lizard, serpent nor 

 bird, escapes; indeed birds are peculiar suf- 

 ferers, witness the too common "gapes" of 

 poultry, a choking of the windpipe by thread- 

 worms, and the numerous parasitic worms 

 which Mr. Shipley's labours have discovered 

 in the well-nigh sacred grouse. Of ticks the 

 shepherd is only beginning to know the full 

 dangers, as of fleas man himself. Apart 

 from bacterial and protozoan pests, as yet 

 beyond counting, man is debited by the 

 parasitologist with at least sixty species; 

 some reckon twice as many. The amazingly 

 varied methods of Nature for the diffusion 



