SOLITARY WASPS OF GENUS SYNAGRIS ROUBAUD. 513 



accident could not happen in the nests of the Synagris sicheliana^ or 

 at least it could not occur so readily, as the cell is not walled up 

 until late. In this respect, therefore, the slow and progressive pro- 

 visioning constitutes an indisputable improvement on the primitive 

 instinct. It is an important step in the evolution of the hereditary 

 habits of the solitary wasps. 



Synagris cornuta L. 



In a third species of Synagris, S. cornuta, we find the expres- 

 sion of a maternal feeling infinitely more defuiite, an instinct for 

 rearing the young still more perfected. This is the third term of the 

 series which will lead us directly to the remarkable rearing habits of 

 the social wasps. 



Nidiiication. — The nest of S. cornuta^ as in the case of the other 

 species, is built by the female, with a yellow earth, a mixture of clay 

 and sand, taken from the borders of brooks in moist places and 

 mixed with saliva. Occasionally the clay chosen is of a gray color. 

 As usual, the male does not participate in any manner in the con- 

 struction of the nest. 



The different cells, in this case also, are built separately, but at 

 periods which ma}^ vary considerably more than for the other two 

 species, on account, as we shall see later, of the peculiar manner of 

 rearing the larvae. The nest is composed of an assemblage of cells 

 which are built separately, but the general structure reveals talent 

 which is unquestionably more perfect than in the other two species. 

 The nest of S. cornuta has scarcely been mentioned except b}?^ E. 

 Andre (1895), who described it very briefly. I have had occasion to 

 observe numerous nests of this species in the Congo where it is seen 

 more frequently than the preceding ones. It builds, moreover, in 

 much more accessible places, under roofs of huts (paillottes), and on 

 the protected walls of dwellings of Europeans, at a little distance 

 above the ground. I was able on one occasion to observe the con- 

 struction of a nest, which was immediately before my eyes on the 

 wall of the laboratory, about 1.50 meters above the ground. 



The first compartment took the form of an oval cell, the bottom 

 of which was slightly more expanded than the part which contained 

 the entrance. Usually there is a short neck near the orifice which 

 is more or less inclined toward the side, to facilitate the entrance of 

 the builder. The prominence of the neck is variable. When it is 

 well developed, the cell may take on the appearance, roughly, of a 

 turbinated shell of a gasteropod. (PI. 3, fig. 2.) Frequently, the 

 neck is lacking, and the entrance is then at the upper part of the cell. 

 The length of the cell is, on the average, 3 centimeters, and the broad- 

 est part 22 millimeters. The wall of earth is much less thick in tliis 

 species than in the case of nests of the other two species of Synagris 

 97578°— SM 1910 33 



