No. 555] SPECIES-FORMING OF ECTO-PARASITES 137 



hundred species of mammals, representing 48 genera, 24 

 families and 5 orders, any special scrutiny of the con- 

 ditions of their distribution among mammalian hosts 

 would hardly be worth while. But such scrutiny can cer- 

 tainly now be advisedly undertaken as regards the dis- 

 tribution among birds. For the Mallophagan host list 

 includes already more than 1,100 bird species, represent- 

 ing 33 of the recognized 35 orders of living birds. The 

 known living bird species number, according to the Brit- 

 ish Museum Catalogue, about 18,500. This catalogue, I 

 should note, elevates to the position of species, or at least 

 to the seeming of species, by cataloguing them binomi- 

 ally, the so-called varieties or trinomiaUy dubbed sub- 

 species of the continental and North American ornithol- 

 ogists; and I have followed this custom in my list— al- 

 though against my belief in its taxonomic implication — 

 for the sake of having a common and universally access- 

 ible basis for the host names. 



Thus one out of every seventeen known living bird spe- 

 cies is now included in the Mallophagan host list, as are 

 625 out of the 2,700 recognized living bird genera, and 

 120 out of the 160 living bird families. As comparatively 

 few bird kinds are still unknown, and as on the other 

 hand only a good beginning has been made in finding 

 and describing the Mallophagan kinds, it is certain that 

 the list of hosts of these parasites will increase rapidly in 

 proportion to the total number of bird species. From the 

 proportion of the number of different bird hosts par- 

 asitized by each Mallophagan species and the propor- 

 tion of bird families and genera already in the host 

 list, I estimate, roughly, the total number of living Mallo- 

 phagan species to be about 5,000. 



From the three Acarinate or Ratitian bird orders, 

 namely, the Rheiformes, or South American rheas, the 

 Casuariiformes or Australian cassowaries, and the 

 Struthioniformes or African ostriches, only five species 

 of Mallophaga have so far been recorded. On the rheas 

 occur three species of Lipeurus, one being found on each 



