524 



THE BIOLOGY OF MARINE ANIMALS 



The nervous supply of the chromatophores is derived from the sympa- 

 thetic system. There are chromatic centres in the c.n.s. and from these 

 centres nerve tracts run through the cord. The efferent fibres have the usual 

 arrangement characteristic of the sympathetic system, and arise from pre- 

 ganglionic neurones in the lateral cord. They enter the vertebral ganglia via 

 white rami communicantes, and form synapses there with post-ganglionic 

 neurones (Fig. 3.1). The fibres continue their course through sympathetic 

 trunks, and finally enter grey rami to reach the spinal nerves, in which they 



Fig. 12.12. The Effects of Interrupting Peripheral and Sympathetic 

 Nerves on Coloration of the Turbot Scophthalmus {Rhombus) maximus 



(a) Darkening of an area of the skin as the result of cutting spinal nerve branches; 

 (b) darkening of an area of the body and chin, as the result of cutting spinal nerve 

 branches and the inferior maxillary branch of the trigeminus; (c) darkening of the 

 posterior region as the result of destruction of the sympathetic chain in the posterior 

 haemal canal. (From Pouchet, 1876.) 



extend to their terminations about the chromatophores in the skin. It has 

 been found that the pre-ganglionic chromatic fibres emerge from the cord 

 at a restricted level, in Crenilabrus pavo, for example, at the eighth vertebra. 

 On reaching the sympathetic chain they take ascending and descending 

 paths, and form synapses with many post-ganglionic neurones along their 

 course. Descending fibres enter the tail and ascending fibres finally enter 

 the head, whence they reach the periphery through cranial nerves. 



The mechanism of nervous control of chromatophores in teleosts has 

 been investigated by nerve section, stimulation and the effect of "autono- 



