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at the same time extending into, and well nigh obliterating 

 the lumen of the intestine, it seems absurd to suppose 

 that such a victim can be in the enjoyment of good 

 health. Physiology teaches us that sooner or later the 

 host must succumb to this permanent interference with 

 the functions of digestion and assimilation. .If the fish 

 does not die in a direct manner from inflammatory action, 

 it becomes so weakened that it readily falls a prey to 

 other enemies. To be permanently successful in the 

 struggle for existence, all the vital powers of the individual 

 must be maintained in good working order. 



As a straw shows the way the wind blows, so do facts 

 that are in themselves sufficiently trifling tend to produce 

 instructive conclusions. One of my early experiences in 

 this matter made a lasting impression upon my mind. 

 Some thirty years ago at the time that I held office in 

 the Edinburgh University Anatomical Museum I noticed 

 in a rivulet near Musselburgh, a minnow moving slowly 

 in the water. It seemed burdened, as I supposed, from 

 a superabundance of roe. Having captured it with the 

 hand, I opened the abdomen, when, to my astonishment, 

 there was no roe at all, its body being abnormally distended 

 by a large tapeworm. Here, therefore, was an instance 

 where, to say the least, much inconvenience had resulted 

 to the host, not, be it observed by overcrowding from 

 many parasites, but from excessive distension by a single 

 entozoon. I have since witnessed similar effects in other 

 animal hosts widely differing in the zoological scale. Thus 

 you may sometimes capture earwigs with enormously 

 swollen bodies, due to the presence of a nematode that is 

 eight or ten times as long as the host itself, and it is not 

 uncommon to find other insects similarly affected. I will 

 mention another curious example occurring higher in the 



