116 N. E. McINDOO 



a. Single olfactory organs. About one half of the sections 

 through the antennae contain no pores; in the other half of the 

 sections it is common to see at least one pore in each section, 

 and occasionally three pores may be observed in the same cross 

 section. The chitin is always more or less striated and in sec- 

 tions stained with Ehrlich's hematoxylin and eosin, the older or 

 outer portion of the chitin does not take the stain, but remains 

 yellowish in color ; while the newer or inner layers assume a light 

 purple color. The thickness of the newer layers varies from two 

 to six times that of the older ones, as may be noted in figures 1 

 to 15 ; the older chitin is represented by solid black, while the newer 

 portion is represented by lines. 



With one exception, the structure of the single olfactory 

 organs is identical with that in adult beetles, already described 

 by the writer ('15). This exception is in legard to the pit with 

 which the pore aperture communicates. In adult beetles the pit 

 is a' ways wide and sometimes extends one-third the distance 

 through the integument, but in the larva of Allorhina there is 

 never more than an indication of the pit : in this respect these 

 olfactory pores are like those in Hymenoptera, also described by 

 the writer ('14b). 



Despite the comparative thinness of sections (5 micra in thick- 

 ness) this dimension is so much greater than that of 'the pore 

 aperture and since the microtome knife seldom passes exactly 

 through this opening longitudinally, it is difficult to find one of 

 these organs which serves well as an illustration. Nevertheless, 

 a few were observed in which the opening could be traced from 

 the outside to where the sense fiber enters it. One good illustra- 

 tion (fig. 1) was found in the antenna, showing all parts of the 

 organ, including the pore aperture (PorAp). Since critics have 

 more or less doubted the existence of this opening, it was con- 

 sidered expedient to have a few photomicrographs made of these 

 organs. This work was done by Mr. J. H. Paine of this Bureau. 

 Using the ordinary photographic plates, the old chitin appears 

 black when photographs are made, thereby concealing the pore 

 aperture; but when a plate sensitive to yellow was used, the pore 

 aperture was photographed quite distinctly. 



