53 [Vol. xxxvi. 



cases of established stragglers, having particular regard to 

 the similarity of habitat in Waterfowl and the contact of 

 feathers between Accipitrine birds and their prey/'' 



Although, in the main, in sympathy with Mr. Harrison's 

 views, the speaker directed further criticism against the 

 idea that the parasites in their evolution have necessarily 

 lagged behind the evolution of the host, and poiated out 

 that the parasites' evolution sometimes appeared to progress 

 pari passu with, and sometimes to progress beyond, that of 

 the host. 



Mr. Iredale : I must congratulate Mr. Harrison upon 

 his lucid exposition of this new feature. With regard to 

 the Petrels, I think Mallophaga must be taken in con- 

 sideration with a good deal of caution, but from the data 

 put forward by Mr. Harrison, they seem certainly worth 

 investigation from the view-point of the systematic ornitho- 

 logist. In the case of odd birds, which are rather difl&cult 

 to place systematically (such, for instance, as Pelecanoides) , 

 they may help immensely. From the superficial study of 

 these birds, this is a wrong location. This genus could not 

 possibly go with the Thalassidromidse (=Hydrobatid8e) from 

 any ordinary study of birds themselves. When we get on 

 to Daption, Thalassceca, etc., these three birds naturally go 

 together if you study the superficial characters carefully. 

 They also come close on to Fulmars, and then Ossifraga 

 follows on. Mr. Harrison goes a step further. Ossifraga 

 (recte Macronectes) stands quite alone, and to put it among 

 the Albatrosses is a big jump. We cannot tell, however, 

 by superficial examination where this form belongs. It 

 stands quite by itself. Its habits and general appearance 

 are very peculiar, and it is therefore possible that by careful 

 study of the parasites a definite clue to its correct systematic 

 position might be obtained. 



An extra word of caution may be interposed. Petrels 



always breed in colonies, and four or five distinct genera 



may occur in the same breeding-district. Consequently, 



there is a very good chance of interchange of parasites. If 



' stragglers " among" the parasites are not frequent under 



