100 



CERTAIN PARASITIC INSECTS. 



sucker of the Pediculus, to the stout chitinous jaws of the 

 Mallophaga, or bird lice, is a sudden transition, but on com 

 paring the rest of the head and 

 body it will be seen that the dis 

 tinction only amounts to a family 

 one, though Burmeister placed the 

 Mallophaga among the Orthoptera 

 (grasshoppers and crickets) on 

 account of the mandibles being 

 adapted for biting. It has been a 

 common source of error to depend 

 too much upon one or a single set 

 of organs. Insects have been classi 

 fied on characters drawn from the 

 wings, or the number of the joints 

 of the tarsi, or the form of the 

 mouth parts. We must take into 

 account in endeavoring to ascer 

 tain the limits of natural groups, 

 all the organs collectively, as well 

 as the internal anatomy and the 

 embryology and metamorphosis of 

 insects, before we can hope to 

 obtain a natural classification. 

 The family of bird lice is a very extensive one, embracing 

 many genera, and several hun 

 dred species. One or more spe 

 cies infest the skin of all our 

 domestic and wild mammals and 

 birds, some birds sheltering 

 beneath their feathers four or 

 five species of lice. Before giv 

 ing a hasty account of some of 

 our more common species, we 

 will give a sketch of the embryo- 

 logical history of the lice, with 

 special reference to the structure 

 of the mouth parts. 



The eggs (Fig. 114, egg of the head louse) are long, oval, 

 somewhat pear-shaped, with the hinder end somewhat pointed, 

 while the anterior end is flattened, and bears little conical micro- 



114. Embryo of the Louse. 



uk 



Mouth partg of the Louse 



