HEER ON THE HISTORY OF INSECTS. 71 



occur in nearly the same numerical proportion as tlie Hymenoptera ; 

 the latter, however, are somewhat richer in species. The Flies had 

 the same proportion in the tertiary period also. I am acquainted 

 with 80 species of Biptera and 87 of Hymenoptera from Radoboj 

 and (Eningen*. The order of Biptera comprises two great natural 

 divisions — the Nemocera [langhornigen] or gnat-like Flies and the 

 Brachocera. At present the first form about ^ and the latter ^ of 

 the species ; there are known 1161 of the Nemocera and 7100 of the 

 Brachocera. The Nemocera were the first to appear, and were fol- 

 lowed a little later by the Brachocera, which at OEningen form only 

 j-, at Radoboj about |, at Aix also about ^, in the amber about ^, 

 whilst at present, as above remarked, they constitute f- of the Bi- 

 ptera. The fact that, in all localities from which we have as yet 

 obtained fossil Flies, the Nemocera so decidedly predominate, clearly 

 proves that this proportion was not dependent on local causes, but 

 that the Nemocera were indeed the oldest amongst the Biptera. With 

 this also corresponds the fact that all the known Flies of the cre- 

 taceous age (15 species) belong to the Nemocera, not any to the 

 Brachocera. The few specimens of Flies from the Jurassic rocks 

 with which we are acquainted are unfortunately so badly preserved 

 that no correct determination of their characters can be arrived at. 



Nor is it very difficult to suggest a reason why the gnat-like Flies 

 \Nemocera^ were the first to appear, and have down to the present 

 time formed the majority of the Fly species. The Brachocera live 

 chiefly on flowering and herbaceous plants ; we see them in crowds 

 basking od the flowers of the umbelliferous and syngenesious plants ; 

 on the contrary, the Nemocera fly about in woods and thickets, and 

 particularly affect damp, watery places. Their larvae live partly in 

 water, partly in damp woody bottoms, in rotten wood, and in great 

 numbers in fleshy fungi ; whilst the larvae of the majority of the Bra- 

 chocera inhabit different flowers, fruits, seeds, and roots, especially of 

 herbaceous plants. Everything, however, points to the fact that in 

 the tertiary period the land was occupied chiefly by tree-like plants ; 

 and further, the many species of willow and poplar, as also the swamp 

 cypress {Taxodium), point to extensive swamps and morasses. If we 

 imagine a widely-extended dark damp wood, traversed by small 

 streams and interrupted by morasses, we have altogether the condi- 

 tions requisite for the gnat-like flies. Of the fossil Nemocera dis- 

 covered at (Eningen and Radoboj, three have lived as larvse in the 

 water, and ten in fleshy fungi ; we may therefore feel assured of the 

 occurrence of such fungi in these ancient woods, although as yet no 

 fossil remains of them are known. There were 47 species also of 

 Flies, and that tco the majority, living without doubt in damp woody 

 grounds and rotten wood. Such damp woodlands were very pro- 

 bably also the favourite resorts of the numerous Pachydermata of 



* I would remark, for those who possess ray work on the Insect-Fauna of the 

 Tertiary Formation of Radoboj and (Eningen, that since its pubHcation I have 

 met mth a considerable number of new species, which will be described in a 

 supplement. The numbers given in the present memoir refer to species known 

 to me down to August 1849. 



