210 THE PRESIDENT'S ADDRESS. 



a gad- or Tsetse-fly, a vampire bat, and every other animal which 

 ever consumes any living portion of another living animal without 

 killing it, is a parasite, while the Ricini, the feather-eating Mallo- 

 phaf/a, and the Dermaleichi, which form the bulk of the microsco- 

 pical preparations of parasites, are not parasites at all, because they 

 do not eat the host, but only keep its hair, skin, or feathers clean. 



Mr. r. Geddes, in the " Encyclopaedia Britannica," scarcely de- 

 fines animal parasites, although he classifies them, but he includes 

 the Mallophaga. 



Megnin, one of the latest writers on animal parasites, says, 

 " Parasites are beings which live at the expense of other living 

 beings." He includes the gnats and that class of creatures, but he 

 also includes the Ricini. 



The popular idea is probably intimately connected with the 

 question of position ; a creature which lives upon or in another 

 living creature is regarded as a parasite whether it eats its host or 

 not, and a perfectly free-living animal, which only attacks some 

 other being when it is in want of a meal, is not looked upon as 

 parasitic. I cannot help thinking that some definition founded 

 more or less upon the popular idea is, after all, the best. Let us 

 take the gnats and mosquitoes as excellent examples ; they un- 

 doubtedly do attack us and suck our blood when they have a chance, 

 but as a rule they are vegetable feeders, and probably of the enor- 

 mous numbers of these annoying Diptera which are born only a very 

 small proportion ever taste blood at all ; they are not most abun- 

 dant where animals are numerous, quite the contrary. The midge 

 swarms to such an extent in many of the wildest glens of the 

 Scottish Highlands that it is hardly possible to stay in the 

 places on a summer evening, unless provided with midge- 

 masks. The mosquito is generally supposed to be a specially 

 southern creature, but this is incorrect ; there is probably no place 

 on the face of the earth where it is found in such count- 

 less myriads as in the Tromsdal, a romantic uninhabited valley in 

 Norway, considerably north of the Arctic circle. This valley is 

 almost without vertebrate life, and is only visited by the Lapps, for 

 a few hours at a time, when they drive their tame reindeer down 

 from the mountains for the inspection of such visitors by the 

 steamers as are prepared to pay for the sight, and have telegraphed 

 to the agent in Tromso to bespeak it ; but in the bright and busy 

 little town of Tromso itself, which is only divided from the Troms- 



