520 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1910. 



AA'liich he possessed of the distribution of the nests leads one to be- 

 lieve that he came out of one of them and returned frequently to 

 the place of his birth. At my suggestion, Mr. Weiss caught this 

 male and in order to recognize him removed his left posterior tarsus. 

 Then he was set at liberty again. For some days the insect, doubt- 

 less because frightened, did not reappear, but the following week he 

 was captured again just as he was returning to make his usual in- 

 spection. It may be said, therefore — and this is a character which 

 distinguishes this species from all other eumenids — that the males 

 of Synagris cornuta are not entirely indifferent to the work of the 

 females ; that they know all the nests that are to be found in a given 

 area; and that they ^dsit them regularly, doubtless for the purpose 

 of seizing the females when they emerge. Except for these brief 

 visits, the males are never seen about the nests. They wander at will 

 outside of habitations in the bush and build no shelter for themselves. 



When two males meet on the same nest they attack each other with 

 open jaws, repel each other with their large pincers, and strive to 

 thrust one another away. The first comer usually maintains the 

 advantage. It is principally for this that the formidable pincers, 

 which are developed on the mandibles, as in the stag beetles, seem to 

 serve. They are probably secondary sexual characters rather than 

 real organs of attack and defense developed by sexual selection, 

 which give those who have them an authority over the nests, and 

 consequently possession of the young females. It is probable, also, 

 that they play some role in copulation. Nothing is more variable 

 among the individuals reared in the same nest than the size and 

 form of these large pincers. Some males are entirely without them ; 

 others have them narrow and short, but very sharp ; while in others 

 again they reach extraordinary dimensions and are provided with a 

 blunt tooth near the middle. They represent a sexual character 

 Avhich is not yet fixed, over which hovers the mysterious phenomenon 

 of variation. 



It is well to remark that this section of the genus Synagris^ which 

 is very sharply differentiated from the others by the form of the 

 mandibles in the males, is also completely separated by these bio- 

 logical characters. It is extremely probable that the mode of feeding 

 the larvse with fragments, which is exhibited by S. coniuta^ occurs 

 among the other species of the same group. Viscount du Buysson 

 (1909) has quite recently made known a nest of &. didieri^ a new 

 species from the Congo, which belongs to the section of 8. cornnta L. 

 and 8. proserpina Grib. This nest is precisely like that of 8. cornufa. 

 From one of the compartments Mr. Didier extracted a larva which 

 was isolated in its cell without any debris of caterpillars which had 

 served as food around it, such as are always found in the case of those 

 forms which do not feed their young with fragments. It may be 



