86 



We then might have identical or closely-allied parasites in 

 two or more related species or in closely connected genera. 

 A generic or even family relationship might thus be shown, 

 and it is possible that a disputed point might be settled in 

 this way. Thus, supposing a genus X appears to be related 

 either to the genus Y or to the genus Z, if X and Y have 

 closely related parasites and those of Z are distantly 

 connected, then support is found for the relationship with 

 Y rather than Z. 



L. Harrison (Parasit., viii., 1915, pp. 88-100), in an 

 article on "Mallophaga from Apteryx, and their significance, 

 with a note on the Genus RallicoJa." deals in an interesting 

 way with the value of these ecto-parasites as showing probable 

 affinities amongst their hosts. 



The following extract from Nature (No. 2330, vol. 93, 

 June 25, 1914, p. 439) shows another interesting phase of 

 this subject: — ''From a paper by Mr. H. Victor Jones in 

 the February number of the Zoologist on certain parasites 

 of birds, we learn that while rooks and the diurnal birds-of- 

 prey — probably owing to the strength of their gastric juices — 

 are practically free from intestinal infestations of this kind, 

 curlews show, on the average, no fewer than 49'5 per head. 

 As there seems to be a connection in many species between 

 the numbers of external and internal parasites, it is 

 suggested that some of the former may serve as hosts for 

 the latter during the earlier stages of their development." 



There is clearly very much work still to be done in the 

 parasitology of Australian birds. I have now collected a 

 considerable number of mallophaga and worms which await 

 description when our few investigators in these subjects have 

 time to consider them. Cestodes have already been described 

 from 44 species of our birds. I record their occurrence in 

 59 species, of which 50 are new hosts. Cestodes, it will be 

 seen from the attached list, are rare in our wild parrots, 

 have not yet been met with in our cuckoos, are common in 

 the honey-eaters, and occur in several of the Ptilonorhyn- 

 chidae, as well as in other genera. I have not found any in 

 the Acanthizas (9 species and 30 individuals) or in Sericornis 

 (4 species and 15 individuals). Here it may be mentioned 

 that, once helminth parasites are "dropped" by a host- 

 species or host-genus, with rare exceptions it is very 

 unlikely that such species or genus will ever again become 

 infested by such parasites. In other words, these parasites 

 are usually so highly specialized that they can only 

 exceptionally adapt themselves to hosts of a quite different 

 kind, and new true parasites derived from semi-parasites only 

 very rarely arise. 



