OUR DOMESTICATED ANIMALS. 3 



injurious effects on the animals they infest. I may, there- 

 fore, dismiss their consideration by referring to my paper 

 " On the Nature of Pseudentozoa found in diseased and 

 healthy cattle/'' originally published in the Lancet for 

 January 1866, and subsequently reprinted in the supple- 

 ment to my treatise on entozoa, p. 40. The affinity of 

 these bodies to the gregarines and other allied forms of 

 protozoa is there fully explained. 



Each species of helminth, entozoon, or true internal 

 animal parasite demands a separate notice;, but I shall 

 dwell at more or less considerable length on those forms 

 only which, either by their presence affect the welfare of 

 the beast itself, or prove injurious to mankind indirectly 

 by operating to prevent our utilising the quadruped's 

 flesh as food. On the other hand I cannot allow the 

 short-sighted prejudices of our so-called practical men to 

 prevent my noticing, however briefly, the rarer forms of 

 parasites. For it must be borne in mind that, although 

 in the present state of our knowledge many of the para- 

 sites of this animal now seem to be of no practical im- 

 portance, yet, by-and-by, future discoveries may impart a 

 very different aspect to the value of known facts which, 

 in consequence of this narrowness of vision, have hitherto 

 appeared to be altogether destitute of interest. 



In the first place, let us consider the nature of those 

 parasites which are commonly called flulces. These crea- 

 tures form the group or natural order of Entozoa, termed 

 Trematoda, or perforated worms. We sometimes speak 

 of them as trematodes, or flounders ; but they are recog- 

 nised more frequently as flukes. A fluke signifies, by 

 virtue of the original meaning of the word, anything flat, 

 and the sailors in the North Seas employ the term "flukes" 

 to designate the flattened division of the tail of the whale. 



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