CHEMORECEPTION 145 



The situation in the butterfly Vanessa indica is not yet so clear. 

 Kuwabara (1951, 1952, 1953) has shown that water, sugar, and some- 

 times sodium chloride elicit proboscis extension. Both sodium 

 chloride and quinine inhibit. There is no behavioural response to 

 acids. Morita et al. (1957) concluded that there were more than three 

 kinds of impulses from this chemoreceptive hair; one neuron respond- 

 ed to sodium chloride, one to sugar; probably there were also fibres 

 responding to quinine and water. A later work (Morita and Takeda, 

 1959) concluded that there were four sensory neurons responding as 

 follows: (1) one responding to concentrations of sodium chloride 

 which were less than M/4; (2) one responding to sodium chloride in 

 the range IM to M/64; (3) one responding to sodium chloride con- 

 centrations greater than M/64; (4) one responding to sugar. Presum- 

 ably there is also a mechanoreceptor. A further analysis of the 

 situation in this insect has yielded the conclusion that the tarsal hairs 

 contain a mechanoreceptor, a sugar receptor, and, in some cases, a 

 sugar-NaCl receptor (Takeda, 1961). In 50 per cent of the hairs tested 

 there was no response to NaCl. No sensitivity to quinine or acetic 

 acid could be detected nor were any other kinds of chemoreceptors 

 found. The only histological evidence bearing on this question is the 

 description by Eltringham (1933) of the chemoreceptive hairs of 

 Vanessa atalanta. No statement is made in this work of the number of 

 neurons associated with each hair. 



In Leptinotarsa there are apparently five receptor cells associated 

 with each hair, but the electrical picture is still unclear. Sodium chlor- 

 ide evokes impulses designated by Stlirckow (1959) as h and n\ 

 potassium, impulses designated as h' and n\ Stiirckow suggested that 

 h and h' originate in anion receptors and n and n' in cation receptors. 

 Water gives isolated low potentials; a sugar receptor is inferred; 

 bending the hair provokes no clear spikes attributable to a mechano- 

 receptor, although there is an unruly pattern of activity; alkaloids 

 associated with plants that are unacceptable as food provoke salvos of 

 spikes from two cells. 



Electrical Events Following Stimulation 



It is clear in all cases thus far studied in detail that the hairs subserving 

 contact chemoreception are compound organs containing a number 

 of chemoreceptors and usually a mechanoreceptor. In the fly at 

 least each chemoreceptor is specifically different with regard to the 

 chemicals to which it is sensitive. In all cases each receptor performs 

 the dual function of reacting to the stimulus and generating nerve 



