172 THE CANADIAN ENTOMOLOGIST. 



ground. The soil was comparatively solid. From the freshness of the 

 leaves which composed the cells it would seem that the work had but 

 lately been accomplished, but after the examination of a few, it was 

 •evident that some time had elapsed, since the larvae had attained to 



• considerable dimensions. 



The cells were nearly three-quarters of an inch in length, with a 



• diameter of one-fourth of an inch. They were constructed of nearly 

 perfect leaves of Spiraea coiymbosa, instead of those of the various species 

 of Rose. The outermost circle of leaves, three in number, had their 

 margins slightly overlapping on the exterior, each piece forming an arc of 

 a circle of 120 degrees. "Within these were other three, arranged 

 alternately with them ; others, again, alternating with the latter, and so 

 on until there were no less than six circles, having eighteen pieces in all. 

 Each succeeding individual layer from without inwardly projected but 

 slightly beyond its predecessor, having but a slight resemblance " to a 

 long sleeve with folds upon it," as has been affirmed by writers. The 

 mouth of each cell was closed by six circular pieces of leaves, nipped 

 from the same plants. These were a trifle larger than the mouth of the 

 cell, and when in position presented a concave surface facing outwardly. 

 It is obvious that the whole structure is a striking proof of adaptation to 



.an end. If the cell had been arranged vertically, its structure would 



• doubtless have afforded water a ready access to the larva and its food, and 

 thus have defeated the object which nature had in view. In the horizontal 

 position the tile-like arrangement in the exterior, acts as a sort of roof by 

 which the water is turned off. The concave arrangement of the circular 

 pieces subserves a similar purpose. The freshness of the leaves was 

 due, no doubt, to the protection which the enveloping earth afforded. 

 The chemical rays of sunlight, which act upon the parenchymatous 

 material of the leaf, when deprived of its vitality, converting the green 



. and granular chlorophyl into others of a brownish hue, operate with less 

 intensity at the depth of three inches. The comparative absence of 

 moisture in the ground, no doubt, prevents oxidation ; there being ample 

 moisture at the same time to insure softness and prevent rigidity. 



During the early part of last April (1874), several cells were brought 



to me by one of my pupils, which, on a superficial examination, appeared 



to be the mud cells of our ordinary Pclopaus, the mud-dauber. They 



were found adherent to the rafters of an unplastered attic. The cells 



^were arranged side by side in numbers of three. On the exterior there 



