208 [August 



no appreciable difierenee, appear at points so situated as to preclude 

 the possibility of any intercommunication." (Ibid. pp. 201 — 239 and 

 p. 239.) 



Since, ls%, it is not denied even by Prof. Agassiz himself, that 

 many plants which cannot be supposed to have been introduced are 

 common to the two continents ; since, 2ndli/, several birds, which can- 

 not be reasonably supposed to have been introduced, for example 

 the common mallard, the blue-winged teal and the magpie, are common 

 to both continents; and since, lastly^ there is a mammal— i/f>mo sapiens 

 Lin. — -common to both continents, though the American variety differs 

 so remarkably from the European one, that if an American insect dif- 

 fered as much from a European one it would undoubtedly be con- 

 sidered as a distinct species; — for these three reasons, arguing a priori., 

 it might be reasonably inferred that out of the vast multitude of insects 

 there would be at least a few species indigenous on both sides of the At- 

 lantic. Yet, owing to the preponderant influence exerted for many years 

 back over American naturalists by Prof. Agassiz, most entomologists 

 in this country have hitherto either tacitly acquiesced in his theories 

 or become devoted believers in them. Hence the American describers 

 of new species of insects have generally been content with ascertaining, 

 that a species supposed to be new had not been hitherto described as 

 American, and have troubled their heads but little as to whether the 

 same species might not have been described as exotic. Had it been other- 

 wise, many more species would probably have been found to be com- 

 mon to the New and Old Worlds than it is possible now to point out. 

 Latterly, however, in two Orders* — Neuroptera and Diptera — the 



* I use the term Orders here aud throughout in the ordinary sense of the 

 term. Agassiz considers Insects, Crustaceans and Worms as the three Classes 

 of Annulata, and Insects he subdivides into three Orders — Winged Insects, 

 Arachnida (Spiders, kc.) and Myriapoda (Centipedes, Ac). What are usually 

 called Orders by Entomologists, are apparently degraded by him into Subor- 

 ders. Dr. LeConte calls the Orders of Agassiz Subclasses, and uses the term 

 Orders in its ordinary sense. Prof. Dana uses the terms Class and Order in the 

 same sense as Agassiz, and calls Hymenoptera, Diptera, &c. tribes, introducing 

 between the Order and the Tribe certain divisions which he denominates subor- 

 ders and ordinules. " Nominum hsec continua subversio," says Latreille, speak- 

 ing of the continual substitution of one generic name for another, "scientiam 

 occidit." (Gen. Cr. et Ins. iv. p. 19.) 



