326 PROCEEDINGS OF THE ACADEMY OF [Apr., 



regarded as the lowest hymenopteron, has the least number of 

 groups of all the species examined, but it stands fourth in regard to 

 the number of isolated pores. Its total number of pores is larger 

 than those of many of the higher forms. Among ants the variations 

 are also great. For the legs of ants the number of pores varies from 

 211 to 356 and for the winged ants the total number varies from 

 463 to 1,090. The smallest specimen among the ants and the second 

 smallest one of all the Hymenoptera examined is a female with 463 

 pores as the lowest number. The drone honey bee with 2,608 pores 

 has the highest number. The smallest specimen examined is a wasp 

 with 688 pores. (For further details see table, p. 332.) 



III. Relative Sensitiveness of Species Examined to Odors. 



It was impossible to obtain a sufficient number of live insects of 

 each species examined so that their relative sensitiveness to odors 

 could be experimentally determined. If such had been possible, 

 the reaction times obtained would prollkbly not represent the true 

 relative sensitiveness better than the method described below, 

 because the reaction times depend not only upon the ability to 

 receive odors, but also upon the agility and sluggishness of the 

 insects used. Using only the grand total number of pores of each 

 species examined (see table, pp. 330 to 334) as a basis, it is also impos- 

 sible to ascertain the relative sensitiveness because the numbers are 

 too variable. Moreover, it may be generally said that the smaller 

 the species the fewer and proportionately larger are the pores. 



The method adopted for determining the relative sensitiveness to 

 odors is: (1) determine the relative sizes of the prepared insects; 

 (2) divide the total area of cytoplasm exposed to the air in all the 

 pores of a given insect by the total area of cytoplasm exposed to the 

 air in all the pores of Microgaster, used as a standard; (3) divide the 

 quotient obtained in (2) by the relative size of the given insect. 

 The number resulting by this division is called the relative sensi- 

 tiveness of the given insect. 



Since it seems reasonable that as a general rule the sizes of two 

 hymenopterous insects are proportional to the respective diameters 

 of their femurs at the extreme proximal ends, the femur of the hind 

 leg of each prepared specimen was measured with the aid of a camera 

 lucida. These measurements may be called the relative sizes of the 

 insects and the diameter of the extreme proximal end of the femur 

 belonging to Microgaster may be called 1.00, as a standard by which 

 to calculate the diameters of the other femurs. It was thus ascer- 



