38' Dr. Karl Krapelin on the Pulicidss. 



group of the Orthoptera, which is certainly not very natural, 

 and their multifarious relations with the Neuroptera, the suc- 

 torial ApidfB, the biting Mallophaga, and lastly the pupal 

 rest of the male Coccidaj, may sufficiently establish this pro- 

 position. It is still worse, however, as regards general avail- 

 ability, with the distinctive characters of the orders generally 

 cited — the segmentation of the thorax and tarsi, the structure of 

 tlie wings, of the different buccal organs, antennae, &c. The 

 mere fact of the agreement or difference of these organs individu- 

 ally cannot give us certainty as to the systematic relationship 

 of two series of forms, but only the examination whether the 

 general organization of one group, as expressed in the deve- 

 lopment of all morphological characters, shows or does not 

 b\\ow jjhyhgenetic relations with those of another group; in 

 other words, whether the observed ditterences in the structure 

 of the parts may be referred equally v/ell to a different '' fun- 

 damental plan " in their arrangement, as to simple changes of 

 form and reductions, such as may be explained by altered 

 function. Self-evident as this proposition appears in the 

 light of modern zoology, the history of opinion as to the sys- 

 tematic position of the flea nevertheless shows very plainly 

 how little it has hitherto been taken into consideration by 

 entomologists. One important aid in such investigations 

 upon the true phylogenetie relationships of forms is unfortu- 

 nately at present still almost wholly shut out from us. I refer 

 to the anatomical structure of the organs. The knowledge of 

 this, and especially that of the generative organs, is at present 

 60 imperfect that a detailed consideration of the internal 

 organization seems to be of little use in the classification of 

 insects. 



After these prefatory remarks upon the principles which are 

 or should be of force in the grouping of insect-forms, the 

 question as to the systematic position of the Pulicidse may be 

 postulated as follows : — Do they or do they not, in the totality 

 of their organs, show near relations of affinity with any of the 

 other groups of insects ? In the former case we should have 

 to arrange them in this group of insects ; in the latter we 

 must establish an independent order for them. 



I naturally commence my examination with that order of 

 insects which, in the judgment of zoologists, has the most 

 right to receive the Pulicidse into it, namely the Diptera. 

 The series of the Diptera must decidedly be called a unitary 

 one ; but the two characters so often brought prominently 

 forward (a perfect metamorphosis and suctorial buccal organs) 

 do not alone establish this unity, seeing that we must also 

 ascribe them to the Lepidoptera, the Apid^, and the male 



