THE NATIONAL INSTITUTION. 
89 
184.1.] 
fifty species of birds, a hundred species of shells, 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 compensate 
in case of extreme necessity, for the transmission, for example, of a number of 
species double that which 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 money, 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 be 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 the goodness to send it to other possessors 
of zoological collections in its country, and invite their attention to it. 
After having detailed these general bases, we have still a few words to address to 
the National Institution for the Promotion of Science at Washington in particu- 
