SOLITARY INSECTS. 179 



tops of houses. Many of the web-footed fowls lay their eggs 

 likewise on the ground, as the terns, and some of the gulls 

 and mergansers. But ducks pull the down from their own 

 breasts, to afford a warmer and more comfortable bed for their 

 young. The hawks, the guillemots, and the puffins or coul- 

 ternebs, lay their eggs on the naked shelves of high rocks. 

 The penguins, for the same purpose, dig large and deep holes 

 under ground. 



It is not unworthy of remark, that birds uniformly propor- 

 tion the dimensions of their nests to the number and size of 

 the young to be produced. Every species lays nearly a de- 

 termined number of eggs. But if one be each day abstracted 

 from the nest, the bird continues daily to lay more till her 

 number is completed. Dr. Lister, by this practice, made a 

 swallow lay no less than nineteen eggs. 



The habitations of insects are next to be considered. On 

 this branch of the subject we shall first give some examples 

 of abodes constructed by solitary workers, and next of those 

 habitations which are executed by associated numbers. 



In several preceding parts of this work, the reader will find 

 some instances of the skill and industry exhibited by insects, 

 for the convenient lodging and protection of their young. 

 These it is unnecessary to repeat. We shall, therefore, pro- 

 ceed to give some examples of a different kind. 



There are several species of bees distinguished by the ap- 

 pellation of solitary, because they do not associate to carry on 

 any joint operations. Of this kind is the mason-bee, so called 

 because it builds a habitation composed of sand and mortar. 

 The nests of this bee are fixed to the walls of houses, and, 

 when finished, have the appearance of irregular prominences 

 arising from dirt or clay accidentally thrown against a wall or 

 stone by the feet of horses. , These prominences are not so 

 remarkable as to attract attention; but when the external coat 

 is removed, their structure is discovered to be truly admirable. 

 The interior part consists of an assemblage of different cells, 

 each of which affords a convenient lodgment to a white worm, 

 pretty similar to those produced by the honey-bee. Here they 

 remain till they have undergone all their metamorphoses. In 

 constructing this nest, which is a work of great labor and 

 dexterity, the female is the sole operator. She receives no 

 assistance from the male. The manner in which the female 

 mason-bees build their nests, is the most curious branch of 

 their history. * 



After choosing a part of a wall on which she is resolved to 



