Clasificación en función a requisitos y características

A p re v io u s stud y (S tub b s & Cobb 1981) f a ile d to d e s c rib e any p o s s ib le s tru c tu re s a s s o c ia te d w ith the p h y s io lo g ic a lly documented derm al l i g h t sense (see Moore and Cobb 1985 a ). A f u r t h e r e xa m in a tio n was c a r r ie d o u t in th e p re se n t study on th e a b o ra l s u rfa c e o f th e arm t ip s . T h is re g io n i s known to be th e most s e n s itiv e to p h o tic s tim u la tio n (S tubbs 1982a). The study re v e a le d a c ili a t e d s tu c tu re beneath th e c u tic le th a t d iffe r e d in s tu c tu re fro m those d e s c rib e d on th e s p in e s and tu b e fe e t. T h is c ili a t e d s tu c tu re w hich may fu n c tio n as a p o s s ib le re c e p to r, was c h a ra c te riz e d by a m o d ifie d c iliu m ( F ig s . 17 and 1 8 ). T h is c iliu m p ro je c te d fro m th e c e ll s u rfa c e f o r le s s th a n 0,5pm and th e m ^ b ra n e appeared to be a tta c h e d to fib r o u s m a te r ia l found b e lw th e c u tic le . T h is fib r o u s m a te r ia l has been d e scrib e d i n d e t a il in t h i s o p h iu ro id by H o lla n d and N ealson (1978) and i s composed o f f ib r e s w h ich ru n p a r a lle l to one a n o th e r in d is c re te b u n d le s w h ich make up th e th ic k b u t d is c o n tin u o u s la y e r o f th e c u t ic le . The v a s t m a jo rity o f th e m ic r o v illo u s caps p re s e n t were detached fro m th e c e lls and th e c e ll s u rfa c e la y between 2-5pms below th e

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c u t ic le . The p re se n t study has shewn t h a t i n th e s m a lle s t segments o f th e arm th e p u ta tiv e re c e p to r c e lls were o n ly a m ic ro n below th e c u tic le b ut n e a re r th e d is c th e re w ere s e v e ra l m icro n s s e p a ra tin g them.

These p u ta tiv e re c e p to rs la c k e d a s ig n if ic a n t c i l i a r y ro o t and were a s s o c ia te d w ith la m e lla e o f membrane i n th e re g io n o f th e c iliu m . The a s s o c ia tio n between these m o d ifie d c i l l i a and th e la m e lla e was c o n s is te n t. They were much more d i f f i c u l t to lo c a te in la r g e r more c e n tra l segments o f th e arm. There i s no p h y s io lo g ic a l e vidence f o r th e fu n c tio n o f th e se p u ta tiv e re c e p to rs b u t a p o s s ib le fu n c tio n based on t h e ir s tr u c tu r e i s d iscu sse d on page 8 5 , I t i s argued t h a t th e y may fu n c tio n as p o s s ib le p h o to re c e p to rs .

S m all b u n d le s o f axons ( F ig . 19) o c c u rre d beneath a l l re g io n s o f e p it h e lia examined fro m tu b e fe e t, s p in e s and th e g e n e ra l body s u rfa c e . They were c h a ra c te riz e d by a re g u la r a rra y o f m ic ro fila m e n ts , sm a ll m ito c h o n d ria and th e re g u la r p a ckin g o f th e axons in t o a b u n d le se pa ra ted by an u n s p e c ia liz e d b u t f a i r l y u n ifo rm c l e f t . No a tte m p t was how ever, made to show th a t any o f th e se axons were

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