INTRODUCTION. u 



physiological type. Among birds the horned puffin 

 (Fratercula corniculata} will be selected. 



Growing from the upper eyelid of this bird is a 

 slender, pointed, black-coloured horn, which in the 

 specimen from which the drawing (fig. 7) was made, 

 measured eighteen millimetres in length : there is also 

 a thin horny scale connected with the lower lid. In 

 the adult bird it is stated that these horns are shed and 

 reproduced annually. 



FIG. 7. Head of the Horned Puffin (Fratercula corniculata] 

 to show the horn growing from the upper eyelid. 



It has already been mentioned that the corneous cap 

 of the cavicorn ruminants is merely modified portions 

 of the integument In the Prongbuck (Antilocarpa 

 americand] the hard cap of the horn is annually shed, an 

 observation first made in 1865 in the Zoological Gardens, 

 London. Subsequently, doubt was thrown on the 

 matter, but it has been definitely settled by the observa- 

 tions of Mr. W. A. Forbes. Thus we are able to furnish 



