THE FLEAS OF NORTH AMERICA 11 



Packard himself, although giving an interpretation of the mor- 

 phology of the fleas now known to be in error in many respects, had 

 this to say about their relationships (61, p. 354) • 



The larva of the Siphonaptera apparently presents the nearest approach of any 

 of the insects now existing to the shape of the primitive Diptera. It is certainly 

 a more perfectly developed larva as regards its external structure and also the 

 position of the brain than any dipterous one, and approaches nearer to our con- 

 ception of the primitive, ancestral, dipterous larva than any other form. 



Packard further says : 



As regards the phylogeny of the Siphonaptera we can only say. with our present 

 imperfect knowledge of their embryology, that they seem to stand nearer to the 

 Diptera than to any other order, and that they must have diverged from the 

 ancestral dipterous 'stem before the existing forms of Diptera had become so 

 extremely specialized as we now find them to be. 



Dahl (9) published in 1898 an interesting paper on the systematic 

 position of the Siphonaptera. He would derive the fleas, the phorids, 

 and the dipterous genus Scatopse from a common hypothetical stem 

 which he called the Archiscatopse. Although, as pointed out by 

 Ewing ( 15, p. 348) in 1924, Dahl's— 



interpretation of the degeneration of the Phorid compound eye into the minutely 

 spined area found in some fleas just above the antennal fossa, is certainly very 

 speculative * * * 



yet his theory is one of the best proposed, and he has given many data 

 in support of it. Particularly convincing is his demonstration of the 

 apparently complete homology between the antenna of certain male 

 fleas and that of Scatopse. Xot only does the antenna of the male flea 

 have the same two basal segments, but the pseudosegments in the long 

 club are the same in number as those distad of the second segment of 

 the antenna in Scatopse. 



Martini (66) in 1922 revived the old theory of the basic relationship 

 of the fleas with the Coleoptera. He pointed out the many homologies 

 between fleas and the genus Oxytelus and gave figures representing 

 cross sections of a flea and an oxyteline in which the fundamental 

 structures are homologized. It should be noted that some of the homol- 

 ogies mentioned by Martini as existing between structures of fleas on 

 the one hand and those of the Staphylinoidea on the other are of a 

 very general nature and doubtless exist between fleas and many other 

 kinds of insects. 



Crampton (7, p. 324) has pointed out the relationships of fleas to 

 the Trichoptera and states that the latter — 



could readily serve as the types ancestral to fleas since they have three-segmented 

 labial palpi, their prothoracic sclerites are as much like those of the fleas as any 

 insects, the mesothoracic and metathoracic coxae of Trichoptera are divided into 

 a eucoxa and meron. and the Trichoptera have cerci and terminal structures sug- 

 gestive of those of the fleas. 



He opposed the theory that fleas could be derived from the Diptera 

 because — 



The labial palpi of fleas are frequently composed of at least three segments, 

 while the labial palpi of Diptera (labella) and Mecoptera are never composed 

 of more than two segments, and therefore could not serve as the prototypes of 

 the labial palpi of fleas. 



He also opposed the theory of the origin of fleas from the Diptera 

 because the latter have no meron iu the metathoracic leg. 



