NO. 14 SENSE ORGANS ON MOUTH-PARTS OF BEE — McINDOO 23 



(a) SPINELIKE HAIRS 



Variety a. In describing the spinelike hairs we shall begin with 

 the most delicate ones and then proceed toward the largest, and 

 we shall carefully examine the anatomy of each variety to ascertain 

 if it is anatomically adapted for receiving odor stimuli. 



In regard to the thickness of the walls, the most delicate variety 

 is found on the epipharynx (figs. 9 A and 10, Ep). These are not 

 typically true hairs, because they do not arise from hair sockets, but 

 from small cones (fig. i A, Con^ which, however, might be regarded 

 as another type of sockets. Of all the hairs, these have the thinnest 

 walls. The walls become gradually thinner from the bases to the 

 tips. These hairs are so small and so light in color that they are easily 

 overlooked. Each one arises from the summit of a small cone whose 

 walls are thick and are dark in color, while the chitin (Ch x ) between 

 the cones is light in color. Chitin is stained little or not at all with 

 Ehrlich's hematoxylin. Flexible chitin is usually light in color, -and 

 when chitin is not flexible it is generally dark in color. For this reason 

 these hairs cannot be bent at their bases but may be bent near their 

 tips; and likewise the cones, which project slightly above the level 

 of the surrounding chitin, are rigid, but since the surrounding chitin 

 is flexible each cone with its hair has considerable freedom of motion. 

 In most cross-sections through the epipharynx showing these hairs 

 the sense cells are grouped together so closely that each hair seems 

 to be provided with either a multinucleated sense cell or with more 

 than one cell, each having only one nucleus. In extremely thin sec- 

 tions where the sense cells are not piled upon one another, however, 

 it is clearly seen that each hair is innervated by a single sense cell 

 (fig. 1 A, SC) having only one nucleus (SCNuc) . In the 21-day-old 

 pupa the hypodermis (Hyp) is comparatively thin. 



Wolff (1875) regarded these cones with their hairs as having an 

 olfactory function, and according to their anatomy they are adapted 

 equally as well for gustatory organs, but since chitin after once 

 formed is dead matter and is not porous, it does not seem reasonable 

 to think of either odoriferous particles or liquid foods being able 

 to pass into the hairs in order that the nerves may be stimulated, even 

 if the walls of these hairs are extremely thin. 



Variety b. This variety is found on the mandibles (figs. 7, 8, and 

 6 B, b t , b 2 and fc 4 ) and on the pharyngeal plate (figs. 9 B and 10, & 8 ). 

 These are short, stout hairs with thick walls. At the proximal end of 

 the mandible (fig. 7, b x ) they are usually bent and about a half of each 

 one lies buried in the chitin surrounding the socket (fig. 1 B, bj. 



