154 



THE SENSE ORGANS 



[CH. 



The Labrum and Epipharynx (figs. 67, 68). 



The epipharynx (fig. 67, ep) is a soft chitinous outgrowth from 

 the under surface of the labrum. It is undoubtedly an organ of 

 taste. The sensory portion consists of two curved rows of tiny 

 circular organs, in the form of yellow specks on the surface. One 

 of these taste-organs is shewn, highly magnified, in fig. 68. It 

 consists of a minute chitinous cone (c) set in the middle of a thick 



c * d 



Ifir 



Fig. 67. Labrum (U>r) and epipharynx 

 (ep)oi Aeschna brevistyla~Ra,mb. ( x 20). 

 Underside, shewing brushes of hairs 

 (br), taste-organs (t) and sensillae. 

 Original, chitin preparation. 



Fig. 68. Section through one of the 

 taste-organs on the labrum of the 

 larva of Aeschna (xlOOO). c cone; 

 en canal; CM cuticle; d disc of hard 

 chitin; mmerve-ending. Methylenblue 

 preparation, after Zawarsin. 



disc of strong chitin of yellow colour (d), and connected with a 

 canal (en) carrying a fine nerve-ending (nv)'. Some of these organs 

 are also found on the surface of the labrum itself. The epipharynx 

 also carries two stiff brushes of hairs (fig. 67, br) pointing inwards. 

 Numerous small scattered tactile hairs occur both on the labrum 

 and epipharynx, and a row of strong hairs along the border of the 

 former organ. 



The Hypopharynx (fig. 69). 



The hypopharynx (fig. 69) is well-developed in Dragonflies. 

 It is a soft chitinous outgrowth from the base of the labium, 

 projecting into the buccal cavity in the form of a distinct tongue. 

 It is usually regarded as an organ of taste. It is, however, covered 

 only with numerous long yellow hairs. Zawarsin [204] has shewn 

 that the nerve-supply of these hairs is of the ordinary kind. He 

 therefore concludes that the hypopharynx is merely an organ of 

 touch in the larva. We think the same holds good for the imago. 



The opening of the salivary ducts lies at the base of the 

 hypopharynx (fig. 45 E). 



