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THE PARASITES OF AUSTRALIAN BIRDS. 



By J. Burton Cleland, M.D. 



[Read May 11, 1922.] 



Apart from the interest centred in themselves zoologically 

 as species and genera of animals, the parasites of birds may 

 claim special attention from ornithologists on several grounds 

 connected with their hosts. It is with the bird aspect that 

 this contribution deals. 



The ecto- and endo-parasites of birds may affect their 

 health. In a state of Nature we have little evidence of this 

 as far as our native species are concerned. Attention may be 

 called, however, to the helminth ova found in tumours in 

 the intestine of a black duck. 



In certain cases, ornithologists may perhaps gain con- 

 siderable help from a study of bird parasites in establishing 

 generic affinities in otherwise doubtful cases. With some 

 exceptions, and excluding occasional accidental infections of 

 birds of other genera, both such external parasites as 

 mallophaga and such internal ones as the helminths are 

 probably remarkably specific as regards their hosts : that is, 

 are confined to one species of bird only or to a few closely- 

 allied species. In a broader sense, this may also apply to 

 genera. The reason for this specification is clear. The 

 ancestors of the parasites undoubtedly began their parasitic 

 career as accidental infestations, individuals gaining access 

 to their hosts in some way, being able to resist the efforts 

 of these hosts to dislodge them, and being capable of nourish- 

 ing and reproducing themselves in their new environment. 

 In the course of time they became structurally more and more 

 modified to fit themselves for the parasitic life. Modifica- 

 tions suitable for one host might be unsuitable for others. 

 Passage would more easily be achieved from one host to 

 another of the same species. During the period in which 

 the parasites were undergoing these marked evolutionary 

 changes, their hosts would also be doing the same. Some- 

 times the parasites would change structurally more quickly 

 or more markedly than their hosts, and then we would have 

 perhaps two or more closely-allied species of parasite in one 

 specific host or in two or in several closely-related hosts. In 

 other cases the parasites might remain more or less 

 stationary, whilst considerable structural changes might occur 

 in several directions in the descendants of the original host. 



