1921] Wheeler: Some Social Beetles 89 



The prominent tubercles on the sides of the pupal pronotum 

 of Eunausihius merit somewhat fuller consideration, because 

 they present a striking instance of the retention in an earlier 

 ontogenetic stage of a character which may be completely lost 

 in the adult. An examination of the common saw-toothed grain- 

 beetle, Oryziephilus (formerly Silvanus) surinamensis L., repre- 

 sented in Fig. 7, and other species of the same genus, shows 

 that the adult beetle has six acute teeth on each of the lateral 

 borders of the pronotum, corresponding to and arising within 

 as many large, blunt tubercles of the pupa. These structures 

 were long ago noticed by Coquerel (1849) and Perris 

 (1852) and by the former erroneously supposed to be por- 

 tions of some tracheal system peculiar to the pupa. In 

 Nausibius {N. clavicornis) the pronotum of the beetle bears 

 six obtuse teeth on each side. In other Silvanid genera, such 

 as Silvanus and CatharUis as well as in Eunausihius and 

 Coccidotrophus these teeth are either altogether absent in the 

 imago, or reduced to the first pair, which form the anterior 

 corners of the thorax. Eunausibius has well-developed teeth in 

 this position but in Coccidotrophus the anterior corners of the 

 pronotum are merely rectangular. It is therefore interesting to 

 find that the pupa of Eunausibius has four well-developed pairs 

 and a fifth vestigial pair of tubercles, that these tubercles 

 decrease in size anteroposteriorly, and that only the first pair 

 gives rise to teeth that persist in the adult. In Coccidotrophus 

 the reduction of the pupal tubercles is carried much further since 

 there are only small vestiges of the three anterior parts of Euna- 

 usibius, none of which gives rise to teeth in the imago. More- 

 over, the second and third pairs of pupal tubercles may be repre- 

 sented by only a single tubercle on one side of the pronotum, as 

 Boving observed (Zoologica III, No. 7). The tubercles are, in 

 fact, so evanescent that they have become very variable, like ves- 

 tigial organs in general. This is seen in Fig. 8 — b to /, represent- 

 ing the prothoraces of five Coccidotrophus pupae selected from a 

 series of fifty specimens. We may safely conclude, therefore, first, 

 that Eunausibius and Coccidotrophus are derived from ancestors 

 which had a 12-toothed pronotum like the species of Oryzae- 

 philus; second that this condition disappeared first in the imago 

 and still tends to linger on in the pupa, and third, that the tuber- 

 cles have a tendency to disappear in sequence in a posteroanter- 



