tq6 The Irish Naturalist. [September, 



Summing up, it appears that the fully-formed nest of the 

 Little Tern is a definitely excavated structure, conical in 

 shape, and partially filled up with a choice selection of " lining 

 shells," on which are deposited two or three eggs, and that 

 frequently a " bare zone " or " girdie " of sand immediately 

 surrounds the mouth of the nest, 



If we now consider how disproportionately large the eggs 

 are when compared with the size of the bird that lays them, 

 it will be seen that a nest shaped like that which I have 

 attempted to describe will offer special advantages towards 

 the process of nidification. For when the eggs are laid they 

 will tend to assume the position in the nest as depicted in fig. 

 2 (6' 6" 6"'). Here it is seen that the pointed or narrow ends 

 fall towards the bottom of the cone, and the broader ends look 

 upwards towards the parent's breast. 1 



In this way the three eggs occupy a smaller space than if 

 they lay on their sides, a condition which allows of their being 

 more completely covered by the parent bird. 



The "lining" shells below, by truncating the point of the 

 cone, sufficiently increase the space for the narrow ends of 

 the eggs to rest upon (fig. 2, i.) 



It is also likely that these shells are heated by the under- 

 lying sand, and that the increase of temperature reaches the 

 lower parts of the eggs either by conduction or radiation, at 

 the same time that the rest of the surface of the eggs is 

 receiving heat from the body temperature of the mother. 



The third illustration (plate 9) is reproduced from a photo- 

 graph. It is taken from nature and shows the nest undis- 

 turbed, with its general surroundings. 



The " bare zone " is plainly seen and tolerably pronounced, 

 being only interrupted by a large "razor" and a "collier" 

 shell, which are seen lying somewhat across its path (plate 9, b). 



The true conception of the depth of the nest and of the 

 position of the eggs, as seen from above, appears somewhat 

 misleading. This is difficult to avoid, being due to the usual 



1 Sometimes only two of the eggs assume this position, the third one 

 lying altogether on its side. See Irish Naturalist, vol. ii., p. 57. Here a 

 nest of the Common Tern {Sterna Jluviatilis) is shown photographed from 

 nature by Mr. Welch, at Me\\ Island, Belfast Lough. The right hand 

 egg is shown lying on its side. 



