G. GENERAL NATURAL HISTORY AND ZOOLOGY. 191 



in the United States, is variegated with brown, yellowish, 

 and grayish streaks, the male alone being a glossy black, 

 with red shoulders. A blackbird is found in Cuba, however, 

 the male of which is undistinguishable from our bird, except- 

 ing in the smaller size, while the female is of a uniform lus- 

 trous black, differing only from the male in the absence of 

 red upon the shoulders. Similar comparative peculiarities 

 are presented in quite a number of West Indian birds. 



MARKS OF DIFFERENCE OF SEX IX EGGS. 



It is stated that the eggs of the common hen, as well as 

 those of many other birds, present certain external character- 

 istics by means of which it is possible to determine before- 

 hand the sex to be hatched from them. Thus the " male" 

 egg has, at its pointed end, small folds and wrinkles, while 

 the " female" egg is entirely smooth, and well rounded off at 

 both ends. 10 C, March 1, 1870, 42. 



PETREL OIL. 



Ornithologists are well aware that certain kinds of sea-fowl 

 belonging to the petrel family are in the habit of disgorging 

 a quantity of oil when captured, and that this furnishes in 

 large part the food with which they supply their young. 

 Many of these species excavate a burrow in the earth, in 

 which their single egg is laid, and the young bird, when 

 hatched, is left for a long time while the parents are abroad 

 occupied in the business of procuring food. The oil in ques- 

 tion, according to some, is obtained from dead and floating 

 cetaceans or fish ; according to others it is a regular secre- 

 tion. In either case the amount is so great that the inhabit- 

 ants of the island of St. Kilda are in the habit of hunting the 

 Fulmar petrel for the purpose of catching it and causing it 

 to disgorge this oil, which is done by dipping the bill of the 

 bird into a small leather bag suspended to the waist. The 

 amount obtained in this way is sufficiently great to furnish 

 an article of export, and it is suggested that it may probably 

 possess virtues corresponding to those of the cod-liver oil. 

 A recent investigation shows that it is soluble in ether, and 

 much less so in alcohol, and has other reactions which place 

 it side by side with the cod-liver oil. 17 A, December, 187. 



