60 PHIL RAU AND NELLIE RAU 



produce a summer brood in the same proportions as the summer 

 brood which we have just analyzed, then these 86 females will 

 in turn produce 172 new young wasps, males and females. Hence 

 the summer brood, by far the more thrifty of the two, can 

 barely reproduce its population without any increase, and that 

 only if we allow nothing at all for the death of the adults as 

 they work in the fields, or for the utter destruction of the nests 

 by man, etc. So if this rate of elimination were typical, (even 

 without, as just mentioned, any elimination in free adult life), 

 the species in this locality could continue for only four years, 

 by which time it would be exterminated. Or if we take the 

 Meramec Highlands winter population as typical, this exter- 

 mination would go on as surely, although more slowly. But 

 we know that these species have continued abundant in these 

 regions for a great number of years. So how is the population 

 maintained? Is there still another brood or two each year, 

 besides those two here analyzed? 22 If so, they must be very 

 prolific to replenish the fast diminishing stock. Some expla- 

 nation must still be advanced to account for the presence and 

 continuance of this large population here. Of course it may be 

 that for some reason our samples are not typical of what regularly 

 occurs in the population. Every care was taken to avoid any 

 injury or abnormal exposure of the material at any time. Since 

 I know of no work similar to this, we can only look to future 

 investigations for comparative data to determine whether these 

 were in all ways typical samples. Of course the two popu- 

 lations came from different localities, but they are so near and 

 so similar in climatic conditions that I can scarcely believe 

 that the differences of locality would cause such different results. 



THE CONTENTS OF THE PIPE-ORGANS, THE NESTS OF 

 TRYPOXYLON ALBITARSIS 



The pipe-organ nests are not so abundant in the vicinity 

 of St. Louis as are the clustered mud cells. This chapter deals 

 with these nests gathered in the early springs of 1912, 1913 

 and 1914. The data for the three years represent 1,282 cells. 

 Since many of the nests were broken in transporting them home, 

 we shall study each season's lot separately in considering the 

 contents, but for the data of the number of cells in each nest, 



22 Ent. News. Vol. XXVI, p. 469-471. 



