212 THE kntomologist's rkcokd. 



necessary conditions that such a settlement is rarely effected. The 

 particular food must be supplied, the temperature, rainfall, drought, 

 etc., must accommodate themselves not only to the imago, but to the 

 various stages of the insect, and it follows, as a matter of fact, that 

 while no animals are so well adapted for a wide distribution, nor show 

 so clearly the various modes by which migration and dispersal may be 

 effected, yet none show more clearly how effectual the organic barrier 

 may be in limiting the range of the species, and rendering nugatory 

 the migration tendency. 



It is not intended to enter here into the wide and general subject 

 of the geographical distribution of insects, except so far as it has a 

 direct bearing on the the more particular phase of distribution to be 

 here considered, viz., the migration and dispersal of such insects as 

 tend to increase the present area of their habitats, either singly or in 

 flocks, and of the possible causes which have led to the migration and 

 dispersal habits now observed. The latter necessitates a consideration 

 of the antiquity of insects. It must be confessed that fossil insects 

 are far too rare to help us much in determining, or affording much aid 

 to the difficult questions connected with geographical distribution, but 

 they arc quite abundant enough to give us a general idea of the great 

 antiquity, not only of the present families, but also of genera, and of 

 the rate at which the forms of insect life have undergone modification. 



Compared with the antiquity of the higher vertebrates, we may 

 state at once that the age of our present families of insects is 

 immeasurably great. In spite of the fact that insects are, in most 

 cases, quite unsuited for preservation by the ordinary processes of 

 fossilisation, there are some strata in which considerable numbers of 

 insects have been preserved. The newest rocks are, as a rule, the 

 most prolific in fossil insects. In the Tertiary strata, the Oligocene 

 rocks of Florissant, a small ancient lake high up in the Colorado 

 parks has produced above fifteen thousand fossil insects, of which only 

 eight are butterflies. From the Upper Miocene of Switzerland, in the 

 neighbourhood of CEninghen, a large number of individuals have been 

 obtained, about 5,000 having been examined by Heor, and these were 

 referred to about cSOO species. Insects of lower Miocene age have also 

 been discovered near Croatia, including termites, dragonfiies, and a 

 butterfly allied to yantssa. The Aix beds (chiefly perhaps Oligocene) 

 have given other butterflies, and from rocks which are probably 

 Cretaceous in these beds has come Coliates, probably the oldest 

 butterfly known. Dragonfiies, crickets, cockroaches, and cicadas have 

 been found in England in rocks of Wealden age ; a Sphingid moth, 

 and insects of almost all orders in the Upper Oolite of Bavaria, and 

 many fossil Coleoptera in the Lower Oolite of Oxfordshire. From the 

 Lias of Gloucestershire, many Coleoptera, Odonata and Orthoptera 

 have been obtained, the families and genera almost identical with 

 those of the present day, and including ( 'arabidac, Mdolonthidae, 

 Telejihoridae, Fllateridae and Cnrcnlionidae among the Coleoptera ; 

 lUattidae and (iryllidae among the Orthoptera ; Agrion, ^Escltna 

 and Lihellula among the Odonata. In rocks of Carboniferous age, 

 Ephemera, BJatta and Scarabaens have been found, also a large 

 Saturniid moth, and in rocks of Devonian age Coleoptera and 

 Neuroptera, belonging to extinct families, but distinctly belonging to 

 these Orders, have also been discovered. 



Brongniart considers that all the Palfeozoic fossil insects may be 



