1841.] THE NATIONAL INSTITUTION. 89 



fifty species of birds, a hundred species of sliells, five hundred species of insects, 

 in parcels of from one to five specimens each, for an equal number of species and 

 specimens — the latter, however, to be only counted in their total. To componsato 

 in case of extreme necessity, for the transmission, for example, of a number of 

 species double that wljich could be returned, the number of specimens received 

 should at least be doubled, without, however, selecting them from too small a 

 number of species. 



III. The Museum of Heidelberg will always send ticketed specimens; that is to 

 say, accompanied by their systematic names and their habits. It expects the same 

 rule to be reciprocally observed. 



It will only accept in exchange two for one, at least of all those invertebrated 

 animals and other specimens not ticketed, which may not in themselves possess an 

 extraordinary value. 



It also requires that the skins should usually contain the bones of the feet and 

 bony heads. 



IV. The two exchanging museums will keep lists of the specimens which will 

 have composed all their exchanges, in order to avoid sending the same species a 

 second time in exchange for new species. Accordingly, both parties will proceed 

 to the exchange of species increasing in rarity, and consequently "in preciousness ;" 

 and will finish by the almost complete acquisition of a zoological collection, well 

 ascertained, of a foreign country. 



V. In fulfilling the conditions two to four, true equivalents may be expected. 

 Small differences of value will be effaced by the continuation of this exchange on 

 a large scale. With regard to the mammiferous and other classes, the acquisition 

 and preparation of which are very costly, specimens of some equality will only be 

 exchanged ; a mouse will not be given for a stag. Should there be some specimens 

 sent of peculiar value, it might be estimated in monej', in order that the nearest 

 equivalent may be chosen. 



VI. The Museum of Heidelberg is subjected to this law : Not to send any thing 

 by way of compensation to an individual before having received the articles for 

 which compensation is to be made. But it may commence an exchange with all 

 public establishments. 



VII. Every museum that may wish to exchange on these bases will inform the 

 Museum at Heidelberg how many species and specimens, and what class of ani- 

 mals, it wishes to exchange, and at what time it may be able to send them ; it will 

 be informed as soon as possible if the particular exchange is accepted or not and 

 when the compensatory exchange will be ready. It should be recollected that pro. 

 visions of zoological specimens can only in general be made among us from the 

 month of March to the end of September, (with the exception of some migratory 

 species of birds, fish, &.C., which arrive in winter,) and that in consequence an 

 understanding should bo had in regard to the exchanges to be made before the com- 

 mencement of the ensuing season. 



VIII. In case the museum to which this annunciation is addressed cannot accept 

 the propositions, it is requested to have tlic goodness to send it to other possessors 

 of zoological collections in its country, and invite their attention to it. 



After having detailed those general bases, we have still a few words to address to 

 the National Institl'tion for the Promotion of Science at Washington in paiticu. 



