SCIENTIFIC SUMMARY. 
333 
At a distance of but three or four feet, the curves will spread out to two or 
three feet in length when a tone is made to which the tube can reasonably 
respond. 
ZOOLOGY. 
Examination of Teeth of Cesti'acions. — Professor Agassiz says, in the 
last paper he wrote, which was one only recently printed by the u American 
Naturalist,” 11 Let me here say that from single specimens of Cestracions, 
obtained in different parts of the world, have been indicated three 
supposed genera based on the conditions of the teeth at different 
periods of age. To show that this should not be accepted as an 
unquestionable result, let me say that I have examined the young of the 
three supposed genera. They are all provided with keeled molar teeth, 
while the adults have the flat grinders supposed to be characteristic of the 
Cestracion type alone. I am therefore satisfied that it is worth while to 
collect largely and preserve a number of specimens, even if they be sharks 
and skates and occupy a great deal of room, in order to learn their history, 
which has just shown of what importance has been the identification of teeth 
among fossils. Thus sharks drop their teeth, and scatter them along the 
bed of the ocean in great numbers, probably ten or twenty times as many as 
they have at one time while living, so that it is not to be wondered at that 
we so frequently find in collections of fossils loose teeth of sharks, and that 
we so rarely find the jaws of sharks with teeth in their places. Of course 
in those species in which the teeth are isolated and do not support one 
another, we should hardly ever expect to find them fossil in position; 
while those which are pressed upon one another may be found in the fossil 
state, and that occurs again and again, and among the fossil fishes there 
are a number of sharks in which jaws with teeth arranged in rows are 
represented.” 
Relation between the Colour of certain Birds and their Geographical 
Distribution. — A communication has lately been made to the Academy of 
Sciences of Paris, by Mr. Alph. Milne-Ed wards, upon the relations existing 
between the colour of certain birds and their geographical distribution, 
having special reference to the fauna of Polynesia. His inquiries have 
embraced not only researches into the absolute fact of melanism in the way 
of black plumage, but also the degree to which this influence has modified 
the true colours. Referring to the fact that birds with black plumage 
are found in all parts of the globe, in certain families of wide geographical 
extent, he states that melanism is exhibited decidedly only in the southern 
hemisphere, and especially in the portion embracing New Zealand, 
Papouasia, Madagascar, and intermediate regions. Thus, in the swans, all 
the species of the northern hemisphere are white; in New Holland, 
however, there is a species that is entirely black; while in Chili and 
elsewhere in South America we have the Coscoroba swan, entirely white, 
with some of the quills black, differing in this respect alone from the allied 
species in China. Again, in speaking of the black parrots, Professor Milne** 
Edwards remarks that none of these are to be found black in America or 
