NONPHOTIC RECEPTORS IN LOWER FORMS 375 



Fig. 10 



FIG. 10. Sensilla basiconica from the antenna of a pupa of the wasp Vespa vulgaris, ch, chitin 

 cuticle; hy, hypodermis ; nl, neurilemma; sc, sense cells; tf, terminal strands; to, tormogen cell; 

 tr, trichogen cell. [From Weber (137).] 



FIG. 1 1 . Diagram showing the histology of a labellar hair and associated cells in Phorima. The 

 large trichogen and tormogen cells are at the left, and three neurons with silver stained processes at 

 the right. The chemosensory area is confined to the silver -stained tip of the hair. The neuron in the 

 middle of the group of three does not have any visible connection with the chemosensory area. 

 [From Hodgson & Roeder (60).] 



receptor cells. The lateral eyes of Lunulus (sOj the 

 stretch receptor cells of crustaceans and the chemo- 

 receptor sensillae of the flies are examples. It has been 

 possible to analyze the functions of single receptor 

 neurons in these simple organs. 



Specific Types of Receptors 



CHEMOCEPTORS. The chemoceptors of the inverte- 

 brates have been identified by physiological experi- 

 ments in only a few cases: in Turbellaria, in which 

 the auricular organs on the side of the head have 

 been studied by Koehler (70) and by Mljller (87); in 

 Limulus by Waterman & Travis (136) and Barber (16); 

 in Crustacea by Hodgson (58); in insects by von Frisch 

 (132), Wigglesworth (141), Frings & O'Neal (45), 

 Frings & Frings (44), Hodgson (57), Grabowski & 

 Dethier (48) and Hodgson & Roeder (60). [This field 

 has been reviewed by Dethier (31), by Hodgson C58) 

 and, particularly for molluscs, by Copland (28).] In 



the turbellarians and molluscs these sense cells, which 

 are located in the epithelium, carry fine hairs covered 

 with mucus. Three types are found in the insects: 

 sensillae placodeae, pore plates described by von 

 Frisch (132); sensillae basiconicae, peg-like hair deriv- 

 atives shown in figure 10; and sensillae trichodeae, hair 

 sensillae drawn in figure 1 1 . They are always supplied 

 by more than one neuron. The covering cuticle is 

 very thin (less than i /x) and only partially sclerotized. 

 The epicuticle has a low lipid content (108). The sur- 

 face of the cuticle is always dry. These receptors are 

 suited for quantitative experimental comparisons of 

 different substances. [This topic has been reviewed by 

 Dethier (31).] Therefore they are important for the 

 general physiology of chemoreception. 



In the vertebrates we distinguish between the sense 

 of olfaction and the sense of gustation. An analogous 

 distinction can be made in the insects but not in other 

 groups. Hodg.son (57) showed that the distinction be- 

 tween olfaction and gustation is unimportant at least 

 on a cellular level, if it is based on the physical condi- 



