508 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1910. 



tirely alone. Observation was not long in demonstrating to me that 

 instinct among these wasps assumed an entirely dilferent form — that 

 throughout the genus it is in full course of evolution toward a higher 

 type, toward the mode of rearing the young so entirely different, 

 which exists among the social wasps. The species of Synagi'is 

 constitute, biologically, a type intermediate between those of the 

 solitary wasps and the social wasps. I shall attempt to show this in 

 presenting the results of my investigations regarding the three 

 species. of the Congo. I have been aided in this work by the devoted 

 zeal of my assistant in the commission, Mr. Weiss, to whom I wish to 

 express at the outset my deep sense of gratitude. 



Synagris calida L. 



This species is not common at Brazzaville. I found only one 

 large nest, which was built in September under the roof of the 

 laboratory of the commission. \Vhen collected in October, this nest 

 measured 12 centimeters in length and about 8 centimeters in greatest 

 diameter. It had the appearance of an irregular mass of earth, 

 without appreciable symmetry, the surface being mammilated by 

 a peculiar rough plastering, in which could be recognized the innu- 

 merable pellets of earth which the builder accumulated for its con- 

 struction. This nest contained 11 cells, with very thick walls, all 

 closed and occupied by young pupse, or by larvse which had already 

 devoured their food and spun their silken cocoons. Like those of 

 all the species of Synagris^ this nest was built of a mixture of 

 yellow clay and sand, mixed with saliva. In accordance with the 

 habits of the eumenids, it is probable that each compartment was 

 constructed separately, and that the common covering of earth was 

 merely a secondary assembling of the separate cells. Mr. G. Vasse 

 brought to the Museum of Paris from Mozambique a young nest 

 of this species which consisted as yet only of the first cell. The 

 nest is someM^hat conical, and about 5 centimeters long and 4 centi- 

 meters across the widest part of the base. The apex is occupied by a 

 large orifice, slightly turned toward one side. Mr. Chevalier also 

 sent one from Krebedje (Fort Sibut), in the Gribingui, which was 

 already finished and quite old, but which contained only six compart- 

 ments, from which all the adult insects had gone. It measured 7 

 centimeters in length and 5 centimeters in breadth. 



I should have known scarcely anything about this wasp if I had 

 not accidentally found in one of the closed compartments of the nest 

 which I collected at Brazzaville a young larva dead and desiccated, 

 with the whole of its store of caterpillars. All the other occupants 

 of the cells were either fully developed larvae which had devoured 

 their food and spun their cocoons, or were pupa3. The caterpillars 



