Bird-parasites and Bird-phyluyeny. 257 



higher suborder occurs upon marsupials. But the parasites 

 of the higher mammals beloug, with the exception of a 

 couple of species found upon rodents in South America, to 

 a family of Ischnocera, to the more specialised suborder. 

 I suggest, in explanation of these facts, that Amblyceran 

 Mallophaga parasitized birds and marsupials before the 

 higher mammals had differeutiated out, and that the parasitic 

 history of the group dates from late Jurassic or Cretaceous 

 times. No Mallophaga have yet been taken from American 

 marsupials, but I am confident that they will be, and I am 

 equally confident that they will prove to be very closely 

 related to the Boopidse of Australian marsupials. I do not 

 ask at present any acceptance for my very speculative state- 

 ment, but I believe that it will be justified when descriptions 

 of forms from American marsupials are available. For my 

 present purpose, I am content to come to much more recent 

 times, and to something upon which I can offer you more 

 substantial evidence. The Ostriches and the Rlieas are 

 separated upon two different continents. They possess 

 Isclmoceran parasites — that is to say, parasites of the higher 

 suborder, — which are distinguished from all other Mallo- 

 phaga by a peculiar asymmetry of the chitinous framework 

 of the head, an asymmetry that can be of no use to the 

 insects. It is very certain that these parasites have had 

 common origin, a fact which not only affords additional 

 evidence of the common origin of the host groups, but 

 which also allows us to set the acquisition of the parasitic 

 habit by the Mallophaga sufficiently far back for all practical 

 purposes. The more specialised suborder was leading a 

 parasitic life at such time as the original Struthious stock 

 became split in two, and the two halves isolated in the 

 Ethiopian and Neotropical regions. 



I wish to touch upon just one more point before I proceed 

 to apply the statements I have already made. I have shown 

 that the general condition of Mallophagan distribution 

 cannot be zoo-geographical, but is, rather, a distribution 

 according to host. Eiids of any family, whether at the pole 



SER. X. VOL. IV. S 



