Characters of Birds' -eggs. 355 



The question as to the best colour of the paper to cover the 

 tablets was a serious one, as it was considered desirable to 

 have a uniform colour throughout, and after many experi- 

 ments a pale neutral grey was found to suit the generality of 

 specimens better than any other. Each tablet has a margin 

 'of a warmer colour, but this is merely a matter of taste. 

 The eggs are fixed to the tablets by a very simple and most 

 ingenious device, for a knowledge of which I am indebted to 

 Mr, Bidwell, and without which it would have been extremely 

 difficult to carry out the plan satisfactorily. When an egg is 

 fastened to a flat board, as it touches at only one point, it is 

 not easy to keep it in proper position until the cement is 

 dry, and it is very liable to break away, with a certain 

 amoimt of injury to the fragile shell. These difficulties are 

 completely overcome by the use of common linen buttons 

 of suitable size. The fiat side of the button is fastened to 

 the tablet, and the other side presents a concave surface in 

 which the egg lies comfortably with a comparatively wide 

 area of attachment, and from which, if necessary, it can be 

 easily removed without any fear of injury. The button is 

 detached from the tablet by passing a knife under it, and 

 then it can be soaked off the e^^ by immersion for a few 

 minutes in water. The cement which has for a great number 

 of years been used in the Zoological Department of the 

 Museum to fix shells upon tablets for exhibition — a mixture 

 of gum arable and gum tragacanth — has been found to 

 answer very w ell for the eggs. 



For the sake of uniformity the eggs are (except in a icyv 

 instances, for special reasons) placed with their long axes 

 vertical, the larger end upwards. 



The main divisions of the series are: — (1) Structure; (2) 

 Number ; (3) Form ; (4) Size ; (5) Texture of surface ; and 

 (6) Colour. The first five divisions occupy the first case. 

 The second case is entirely devoted to illustrations of the 

 sixth division. The whole collection consists of about 280 

 specimens. 



Structure is illustrated by a drawing of the well-known 

 diagrammatic section of the newly-laid e^^ of a bird, to be 



