12 THE PHYSIOLOGY OF INSECT SENSES 



At each moult, when new receptors arise to service the increased 

 body size, they, just like regenerating receptors, send axons centri- 

 petally to the central nervous system (Fig. 4). Whether or not the 

 axons fuse when they come together is still in doubt. Pringle (1938 a) 

 was of the opinion that fusion did occur in the cockroach, but 

 Wigglesworth (1953) felt that the matter was in doubt in Rhodnius. 



Fig. 5. A small area of the integument of a fourth-stage larva of Rhodnius 

 showing hairs and neurons. The number of axons present in each nerve 

 as calculated from the number of sensilla is indicated by the figures. The 

 inset shows the distribution of epidermal cell nuclei. (Redrawn from 

 Wigglesworth, 1953.) 



He showed in Rhodnius (Wigglesworth, 1959) by making a rough 

 count of the numbers and types of sensilla on the antenna and a count 

 of the axons in the antennal nerve that there must be a fusion of at 

 least fifteen sense cells to one axon. Similar counts in the leg indicated 

 that similar fusion of the tactile fibres here does not occur. He pointed 

 out that a lack of fusion is understandable in view of the need of 



