291 Dr. J. H. Blasius on the Diversity in the Estimate 
On the side of the majority stands, besides all other ornitho¬ 
logists, BrehnFs ‘Lehrbuch/ published in 1823; on the other 
side stands Brehm alone, in the ‘ Naumannia' and the f Vogel- 
fang’ of the year 1855. So far as any conflict of principles is 
in question, therefore, we have to do with a struggle between 
the entire science of ornithology up to the present time, and the 
most recent views of Brehm. The contradictions depend essen¬ 
tially, although not entirely, upon this conflict of principles. 
The previous estimate of the European Ornis falls into two 
series of very different values—the species regularly inhabiting 
Europe, and those accidentally visiting that continent. The 
species not regularly belonging to Europe require merely a sort 
of police-notice, or domiciliation—we have simply to do with 
the question whether we shall give a place in our books and 
catalogues to the exotic species which may wander into Europe, 
or pass them by unnoticed. If they be left unnoticed, the ques¬ 
tion as to the estimation of the European Ornis becomes greatly 
simplified. 
If, as is almost universally the case, the stray immigrants are 
to be noticed, their acceptance depends simply on the proof of 
their voluntary appearance in Europe, without importation. 
Imported birds, or exotic birds escaped from confinement, have 
no right to a place in our Ornis. The occurrence of Spiza ciris, 
L., in England, of Parra jacana, L., in the south of France, of 
Nycterodius violaceus, L.,in England, of Plectropterusgambensis in 
France, of Erismatura ferruginea, Eyton, in Belgium, of Halieus 
sulcirostris, Brdt., and of many birds commonly kept in aviaries, 
may remain unnoticed without the least objection. 
The number of voluntary immigrants, the occurrence of which 
in Europe is positively ascertained, amounts at the present mo¬ 
ment to a little over 100 species. It has become greater nearly 
every year, and may be expected to continue increasing. 
These species are distributed as follows, according to their 
native countries and the various natural orders :— 
