142 FLEAS, FLUKES AND CUCKOOS 



flamingoes is that these genera were already established on an ancient 

 Anseriformes-stock before it gave rise to the flamingoes on one hand, and 

 to the modern ducks, geese and swans on the other. This would mean 

 that the flamingoes are more closely related to the ducks and geese than 

 to the storks and herons, and, hence, should be included with the 

 former in the Anseriformes and not in their more usual position with 

 the Ciconiiformes. The ostrich [Struthio camelus) of South Africa and 

 the rheas [Rhea americana and Pterocnemia pennata) of South America 

 provide a similar case. In modern classifications it is assumed that 

 these birds are not closely related and hence they are placed in 

 separate orders, the Struthioniformes and the Rheiformes. Both the 

 ostrich and the rhea, however, have closely related species of a genus 

 of Mallophaga [Struthiolipeurus) which is found on no other bird. This 

 strongly suggests that the rheas and ostriches must have shared a com- 

 mon ancestor, also parasitised by the genus Struthiolipeurus, and that 

 this genus was in existence in its present form before the separation of 

 the continents of S. Africa and S. America. 



These two examples are instances where the evidence from the 

 parasites apparently conflicts with the evidence from the anatomy of the 

 birds. Has the evidence been incorrectly interpreted by the ornitholo- 

 gist or the parasitologist ? Here we can discuss only how the latter may 

 have been mistaken, and for this it is necessary to consider the possible 

 factors which may have influenced and obscured the original evidence, 

 and thus misled the parasitologist. 



Discontinuous distribution. We have already discussed (p. 134) the 

 discontinuous distribution of certain genera of Mallophaga. If we are 

 trying to deduce relationships between different birds from the fact that 

 they are parasitised by the same genus of Mallophaga, it is at once 

 obvious that genera which show a discontinuous distribution may be 

 misleading. Passerines and game-birds in this country are both para- 

 sitised by species of the genus Menacanthus, but this does not suggest a 

 close relationship between the two orders, for we also find species of this 

 genus on the tinamous (Tinamiformes) of S. America, the plantain- 

 eaters (Musophagidae) of Africa, as well as the woodpeckers of this 

 country, while related genera are found on other orders. This suggests 

 that Menacanthus was once widely distributed throughout the whole 

 class of birds, but is now extinct on most orders. 



