212 the president's address. 



Mistletoe, the Orobanche, and the Dodder regarded as parasitic, 

 but the fungi of favus and ringworm, the muscadine of the silk- 

 worm, the pathogenic bacteria, &c, are looked upon in the same 

 light ; although they are parasitic, not upon other vegetables, but 

 upon animals ; and it certainly would appear strange if such forms 

 as Saprolegia were not considered parasitic when attacking the 

 Salmonidce, but other allied species when attacking vegetables in a 

 similar manner were parasitic. On the other hand, Van Beneden 

 has very properly said that if vegetables feeding upon living 

 animals are parasitic, then it is unscientific not to consider animals 

 which feed upon living vegetables as also parasitic ; and he conse- 

 quently suggests that there are more animals which are parasitic 

 than which are not so. It may be well worth considering whether 

 it would not be better to confine the term parasites to organisms 

 which are parasitic upon other organisms belonging to the same 

 natural kingdom ; if this be not done, and if we admit with the 

 various writers that in order to be a parasite it is not necessary to 

 reside upon or in the host, that it is not necessary to feed entirely 

 or usually on the host, or always on the same host ; or that all 

 individuals of the parasitic species should ever seek assistance from 

 the host at all, occasional repasts by scattered individuals being 

 sufficient, then we should arrive at the somewhat startling con- 

 clusion that most animals are parasitic, and that the non-parasitic 

 are rare exceptions almost confined to predatory creatures. The 

 caterpillar would be parasitic upon its food-plant ; the bee and the 

 butterfly upon the flowers they suck ; the cow and the sheep upon 

 the grass they eat ; and we cannot be sure that even man himself 

 might not be held to be parasitic upon such organisms as fruit- 

 trees and Brussels-sprouts. 



Now let us glance shortly at how parasites have been classified. 

 Van Beneden first separates messmates, which he divides into fixed 

 and free ; then he separates mutualists, which he does not divide ; 

 finally he comes to parasites, which he divides into those which are 

 free during their whole lives, those that are free while young, those 

 that are free when old, and those which are not ever free. Leuckart 

 distinguishes first between ecto- and endo-parasites; the former he 

 divides into two sections, viz., temporary and permanent ; the latter 

 into three sections, viz. : (1) those having wholly free-living 

 embryos ; (2) those having embryos passing through a different 

 host ; and (3) those without any free-living period passing their 



