82 Annals Entomological Society of America [Vol.1, 



I have elsewhere indicated my belief that the group originally 

 came from some division of the Heteroptera and I am still skepti- 

 cal concerning the recent attempts to relate them to Mallophaga, 

 but for the present study this point is not essential. Granted a 

 primitive form assuming the parasitic relation to some primitive 

 mammal and we have the materials on which to construct a ten- 

 tative phylogeny which we may test by such evidences from mor- 

 phology, distribution and habit as may be available. 



There are of course at least two plans on which we may ac- 

 count for the present distribution of the species of this family. 

 One that the primitive parasitic form appeared at some time in 

 the early history of the mammalian stem and that its subsequent 

 history and the divergence of the various species has gone along 

 parallel with the divergence of the host forms ; the other that it 

 appeared much later in history after the establishment of the 

 mammalian groups and that from an establishment on some one 

 group of animals it migrated to other mammals and the various 

 species developed on new hosts by more recent evolution. The 

 fact that most of the species have a single host to which they are 

 restricted gives unusual opportunity to test any theory of evolu- 

 tion. 



Confining ourselves to the Pediculidas, although it would be 

 interesting also to examine the relation of the Polyctenidaj occur- 

 ring on bats, we have a group showing very clearly a common 

 origin and possessing some very homogeneous characters, the 

 most evident the single jointed rostrum and the single clawed 

 tarsi. The separation of the genera has always seemed somewhat 

 arbitrary and based as a matter of necessity in such simple forms 

 on rather trivial characters, but some of these characters take on 

 entirely new significance if correlated with the distribution of the 

 genera with reference to their hosts. 



It will be noticed from the diagram (PI. II) that the groupings 

 of these parasites bear a distinct relation to the main divisions of 

 the class of Mammalia. While this is not presented as an accurate 

 statement of the phylogeny of the mammals, nevertheless it repre- 

 sents the remoteness of some of these groups and illustrates some- 

 thing of the possible relationships between them. Assuming that 

 the primitive parasitic group established itself on a primitive 

 mammal, we can follow the divergence of the different groups 

 with considerable assurance. There is a distinct type belonging 

 to the group of rodents, another for the insectivora, another for 



