On Flukes. 25 



when he first "beholds it ; and words fail to express the peculiar 

 feeling of awe and aversion of Nature which creeps over him 

 when he discovers the thing, that appeared to him incredible, to 

 be a simple matter of fact." 



Nearly thirty years have elapsed since the Russian professor 

 penned this prologue, and it must be conceded that our recent 

 helminthological discoveries have, as yet, done little calculated 

 to chase away such prejudice from the public mind. Perhaps, 

 of all the paradoxes enunciated by creative wisdom — in so far as 

 they affect the economy of organic being — none are more likely 

 to excite astonishment than the truths which demonstrate the 

 curious phenomena of parasitic life ; yet, we make bold to num- 

 ber ourselves with those who believe in " necessary evils," and 

 in the following pages undertake to show how a nearer acquaint- 

 ance with the objects of our study can impart that " enchantment 

 to the view" which is commonly regarded as an effect of 

 distance. 



The first group of parasites to which we invite attention are 

 the "flukes," as they are popularly termed; but not unfre- 

 quently we shall speak of them as trematodes, or Entozoa of the 

 order Trematoda, which signifies that they are internal para- 

 sites, suctorial worms, or helminths, generally characterized by 

 the possession of certain pores or openings. The Greek word, 

 Tp7]fMarcoSr]<i } from which the ordinal title is derived, means per- 

 forate. Other parasites, it is true, display a variety of openings 

 and sucking disks, but we shall find them associated with 

 several distinctive peculiarities, into the consideration of which it 

 were now a loss of time to enter. 



Flukes are not parasitic during the entire period of their 

 existence, for whilst passing through the cycle of their life- 

 development, they frequently change their residence, at times in- 

 habiting either open waters or the dewy moisture of low pasture 

 grounds. Their strange migrations, active and passive, from 

 parasitic to non-parasitic abodes, will be discussed hereafter. 

 In the adult condition flukes abound in all classes of vertebrated 

 animals ; that is to say, in fishes, reptiles, birds, and mammals. 



To convey a more precise idea of their distribution, we may 

 observe that flukes are sparingly found in man and monkeys. 

 They are still less frequent in the higher carnivora; none, to 

 our knowledge, having hitherto been detected either in the lion 

 or the tiger. In the common cat, however, two species are 

 known, one proper to its wild, and the other to its domesticated 

 state. Only a few infest the dog and fox, and they are almost 

 entirely absent from the civets and ichneumons ; the exception 

 to the rule occurring in the Indian Viverra, in the lungs of which 

 the writer has discovered a small species. 



Flukes are abundant in the nocturnal bats ; they are scarcely 



