110 Proceedings of the Royal Society 
dentition of a foetal Narwhal 7J inches long, in which I found two 
dental papillae developed in the gum, on each side of the upper, 
jaw, but the early stage of development of the foetus did not 
permit me to say whether the anterior or posterior denticle would 
have been the one to become the maxillary tusk, though I thought 
it probable that the more anterior would become the tusk. 
In this much larger foetus the superior maxilla was 8| inches 
long. At the anterior end of each of these bones were two well 
marked sockets, one opening immediately behind the other. The 
anterior socket contained a cylindriform rudimentary tusk. The 
posterior socket contained an aborted tooth J inch long, and 
inch in its widest diameter. The hinder half of the aborted tooth 
was attenuated, and had several short irregular processes projecting 
from it ; the anterior half was smooth and rounded. This tooth 
was inclosed in a distinct sac, formed of fibrous tissue, which, like 
the sac of the rudimentary tusk, was firmly united to the fibrous 
tissue of the gum. There can be no doubt, therefore, that I was 
right in my conjecture that the more anterior dental papilla 
becomes the tusk of the Narwhal. 
3. Observations on the Zodiacal Light. By C. Michie Smith. 
Communicated by Professor Tait. 
While engaged in cable work in the West Indies, I had, during 
the winter and early spring of 1875, a number of very favourable 
opportunities of examining the zodiacal light, 
Before leaving this country I had, under the advice of Professor 
Tait, and with a note of recommendation from Professor Jen kin, 
applied to the Royal Society for the loan of a spectroscope, to make 
observations with during the voyage ; but unfortunately I was 
unable to obtain one, and so had to content myself with a small 
pocket-spectroscope. On the outward voyage I did not notice the 
light at all till we got well to the south, near Cayenne, on the 8th 
of January ; and, owing to the very bad weather we had about that 
time, I was not able to make any satisfactory observations till we 
were again somewhat farther north. The general appearance of 
the zodiacal light has been so often described, more or less faith- 
fully, that I need not attempt any description of it here. I wish, 
