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Parasitism. 

 Address of the President, A. D. Michael, F.L.S., F.R.M.S. 



{Delivered Feb. 24th, 1888.) 



Among the descriptions which explain the nature of the objects 

 shown at this, and most other, microscopical societies, there pro- 

 bably is not any more frequently found than "parasite of some 

 creature," as, for instance, of the horse or the fowl. This is natural 

 enough, for parasites are usually, and almost necessarily, of small 

 size as compared with their hosts, and fall within the range of those 

 studies which cannot be pursued without the aid of a microscope ; 

 moreover, the worker with that instrument, while he shares the 

 horror of parasites which is common to most civilized human beings, 

 still feels irresistibly attracted by their curious and exceptional life- 

 histories, and has a strong tendency to collect and exhibit them. 

 Possibly familiarity breeds indifference. I well remember that 

 when our late lamented President, Dr. Cobbold, exhibited living 

 larvae of that terrible entozoic worm, "the Bilharzia" at the Lin- 

 nean Society, he could not understand why men were not particu- 

 larly anxious to approach his microscope and bottles. In the lists 

 issued by the dealers in microscopical objects will be found long series 

 of parasites and their eggs ; yet probably not one in fifty of those 

 who exhibit and deal in these things ever really considered what he 

 meant by a parasite, and the greater number would be somewhat 

 astonished if they were informed that, according to the views ex- 

 pressed by eminent authorities, most of the creatures which they 

 exhibit are not parasites at all ; while many animals are entitled to 

 that appellation which are not included in our exhibitors' lists. It 

 may, therefore, be worth spending half-an-hour in endeavouring to 

 obtain rather clearer views as to what a parasite is, and in reviving 

 our recollection of a few of the more interesting forms of parasitic 

 life. We have to ask, lstly, can we define the popular idea of a 

 parasite ? 2ndly, does it agree with the scientific idea, or rather 

 with any of the scientific ideas? 3rdly, if it do not, which, if 

 either is correct? It is strange to see how men's views have varied 



