372 THE CANADIAN ENTOMOLOGIST. 



2. Prolificacy. There are numerous species with no par- 

 ticular physical efficiency. Some of these latter owe their ex- 

 istence largely to prolificacy. The common river shad, for ex- 

 ample, may produce from 60,000 to 156,000 eggs, while a seventy- 

 five pound cod may contain 9,100,000 ova. This extraordinary 

 prolificacy is evidently a provision of nature to offset the numerous 

 perils threatening the fry. Some of our plant-lice attain the same 

 end by producing a number of generations annually. For example, 

 the common hop plant-louse is capable of producing twelve genera- 

 tions in a season, the final progeny amounting to over ten sextillion. 

 The increase in this latter species is by geometrical, not arithmetical, 

 progression. 



3. Evasive adaptations. There are hosts of species which 

 escape extinction by the exhibition of more or less cunning in 

 avoiding the many natural perils. This may be the result of 

 modifications in the biology, peculiarities in habit, specializations 

 in structure, or even cryptic or other resemblances. We have 

 sometimes wondered if these factors, physical development or 

 strength, prolificacy and evasive adaptations could be assigned 

 sufficiently exact values that, if two were known, the third could be 

 ascertained. 



The gall midges exhibit a most interesting condition. The 

 approximately 800 American species known probably represent 

 only one-third to one-fifth of our fauna. Some 450 species have 

 been reared from 183 plant genera representing 65 plant families.- 

 The largest of the gall midges is only about one-fourth of an inch 

 in length, while the smallest measures scarely one-fiftieth of an inch. 

 Local in habit, slow of flight, fragile in structure and far from attain- 

 ing an extraordinary prolificacy in many instances, how do these 

 multitudinous species maintain themselves? Ph^^sical develop- 

 ment, either aggressive or defensive, is hardly worth mentioning. 



Biological adaptations. There are good reasons for believing 

 that gall midges are allied to the fungus gnats or Mycetophilida^, 

 many of which live as larvae in decaying organic matter. The 

 inner bark of various trees in incipient decay may contain hosts of 

 Miastor and Oligarces larvae. These maggots are remarkable 

 because they exhibit a modification of parthenogenesis known as 

 paedogenesis, an adaptation of inestimable value to species living 



