60 ANIMAL INSTINCT AND INTELLIGENCE 
of the eggs or young, are often associated with that for nest- 
building. Of this the Eider-Duck (Somaterta mollissima, fig. 
1063) may be taken as an example. Egg-laying and _ building 
are here not consecutive acts, but 
the former takes place at intervals 
during the latter, in a somewhat 
variable fashion. Three succes- 
sive stages are shown in the illus- 
tration, which is taken from photo- 
graphs by Mr. R. A. L. Van 
Someren. The first represents 
four eggs resting in the incom- 
plete nest, and the second (on a 
larger scale) the complete down- 
lined nest with its full complement 
of eggs. The third figure shows 
the same nest during the tem- 
porary absence of the mother-bird, 
and illustrates an interesting as- 
sociated instinct. Before leaving 
her duties she had pulled the 
down over the eggs, so as to 
cover them completely, an act dis- 
tinctly conducive to their welfare. 
For, snugly tucked up under their 
‘eider-down quilt”, they were not 
only kept warm, but also, as the 
figure clearly proves, effectively 
screened from observation. 
But although nest-building is 
almost certainly instinctive in the 
main, it is subject to modification 
in individual cases in ways which 
vouch for the intelligence of the 
%. builders. And such modification 
ee “ane affect the style, materials, 
and place of construction. Often- 
quoted illustrations are those of the House-Swallow and House- 
Martin, which have taken advantage of the evolution of human 
civilization so far as concerned with domestic architecture. 
