46 THE PHYSIOLOGY OF INSECT SENSES 



regions of the dendrites are naked, that is, not invested by Schwann 

 cells, and embedded in the connective tissue matrix. There are no 

 connexions with the collagen-like connective tissue fibrils. They 

 resemble very closely the sensory terminations of the vertebrate 

 muscle spindle and Pacinian corpuscle. 



In Orthoptern (Acrididae) a pair of muscle receptor organs is present 

 in each of abdominal segments one to ten in the region of the mid- 

 dorsal line. The receptor organ is usually attached to the medial edge 

 of one of the longitudinal muscle bands, although it may be nearer the 



Fig. 36. Dorsal longitudinal muscles of the third and fourth abdominal 

 segments of a pupa of Antheraea pernyi, with a part of the band in the 

 fourth segment removed to show the receptor. Motor and sensory 

 innervation of the receptor are shown. (Redrawn from Finlayson and 

 Lowenstein, 1958.) 



middle. Each consists of a large multipolar neuron surrounded by a 

 thick nucleated capsule and a modified muscle fibre. There are also 

 many neurilemma cells. The muscle fibre originates near the anterior 

 end of the segment, and is inserted on the anterior end of the following 

 segment. The fibre possesses striations. Attached to it are numerous 

 thick connective tissue fibres which also extend to adjacent muscle 

 fibres. The axon of the receptor joins the ventral branch of each 

 segmental tergal nerve. 



The most complex receptors are those in the larvae, pupae, and 

 adults of Lepidoptera. In the larvae there is a pair in the meso- and 

 meta-thorax and abdominal segments one to nine (Fig. 36). They are 



