March. 1919.] Review. 105 



theory recently advanced by Dr. Wheeler 1 and by E. Roubaud 2 to 

 the effect that the origin of social habits of insects may be traced to 

 the secretion by the larvae of fluids eagerly sought after by the adults. 

 Dr. Bequaert questions whether the conditions of social life of Be- 

 lonogastcr, the absence of true workers, etc., are very primitive, as 

 thought by Roubaud, or are degenerate. A curious and interesting 

 habit of these wasps is that of gnawing away discarded portions of 

 the nest and reutilizing the material to build new parts. 



Polybioidcs (Epiponinse), of which there are two species, are the 

 only African wasps that enclose their comb in an outer paper en- 

 velope. The comb is vertical, several parallel layers hanging within 

 the envelope. These are the only Vespidse that normally utilize both 

 sides of the comb to build cells, as does the honey-bee. The nests 

 of both species are illustrated by excellent photographs. These wasps 

 are very bellicose, and are uncomfortably prominent features of the 

 Congo region. The nests may reach three feet in length. 



The Ropalidiinse are represented by the genus Ropalidia [=.Icaria] 

 which, with its forty-one species, is the largest of the four genera in 

 Africa. However, only twelve of these inhabit the mainland, the 

 others being found in Madagascar. It builds open combs resembling 

 those of Polistes. Some of the species are very common. These 

 three genera are all restricted to the Ethiopian and Oriental, or in 

 the case of Ropalidia also Australian regions. The fourth genus of 

 social wasps is the cosmopolitan Polistes, which is well represented. 



The large number of species of subfamily Eumeninse (1,900 from 

 all regions) form a dominant, plastic group, and, like all such groups 

 which are undergoing active evolution at present, are peculiarly diffi- 

 cult to deal with taxonomically. Dr. Bequaert's discussion of the 

 characters and variation within this group, and his arrangement, for 

 comparison, of the species of Odynerus and Synagris in color groups 

 are illuminating. 



The exclusively African genus Synagris is one of the largest, 

 most common, and by reason of their large size and brilliant color, 



1 A Study of some Ant Larvae, with a Consideration of the Origin and 

 Meaning of the Social Habit among Insects. By William Morton Wheeler. 

 Proceedings of the American Philosophical Society, 19 18, 57: 293-343. 



2 Recherches biologiques sur les guepes solitaires et sociales d'Afrique. 

 Ann. Sc. Nat. Zool., 1916 (10), 1: 1-160. 



