678 



Couiparative Annual Physiology 



siirfac-c (rcticLihitc) results in its imparting its tint to the animal. The fore- 

 ooing meelianism of aetion (eoneentration and disjiersion of pigment) is 

 lefeiied to as plusiological color change. The chromatophores may also in 

 Ihicncc the coloration of an animal through their accumulation or production 

 of pigment or iheir loss or destruction of it. This mechanism of aetion is 

 known as mor|)hological color change. 



Physiological Color Changes. Chromatophores are of two major types. 

 One t\|ie is seen among the cephalopod molluscs and is a complex organ 

 with a |iigmenl-containing component, the changes in h)rm of which result 

 from the acti\ it\ of numerous radialK -arranged smooth muscle fibers acting 

 sxnchronoLish (fig. 254). The second, more common type, is found in 

 most color changing species. It comprises a single cell or small s\ne\tium, 

 usualK of highly branched outline, and within which pigment distribution 

 is altered b\ streaming movements. 



Fi<4. 2">4. I hf ccpii.ilopdcl clinunatophorf with a, piynicnt concentrated and h, 

 piyintMit disjicrsftl. F roin Bo/ler."' 



I he chromatophores of the cephalopods are highly organized groups of 

 cells, fiach comprises a central uninucleate cell Filled with pigment and pos 

 sessing a highb elastic cell membrane."' Radiating out from the central cell 

 in the plane ol the skin are from d to 20 or more uninucleate smooth- 

 muscle libers. All the (ibcrs ol a chromatophore usually contract simultane- 

 ously, stretching out the small, s]iherical, central, pigmented cell into a disc 

 having a diameter (ifteen to twentx times that of the original sphere. The 

 sjiherical hirm is restored by the el.isticity of the membrane of the central 

 |)igmented cell alter relaxation ol the radiating hbers. A single nerxe Hber is 

 saitl to SLippK each muscle llbcr;'" its terminal arborizations disperse broadly 

 n\v\- the siiil.ice ol the muscle. ,\o motor ;'nd pi. iti's are jiresent, and curare 

 IS reporU'd to be inellectixe in blocking iutnous activation. I he musck libers 

 show .1 rapidity ol contraction to electrical stimuli approaching that of striated 

 muscle lilx-rs C h. ki . 



Little or nothing is known ahoiil the chemical nature of the pigments of 

 cephalopods. Octopus possesses two kinds of chromatophores, one contain- 

 ing .1 leildish blown pigment, and the other a yellow. The sc|uid, / o//go, has 

 three ivpes; hidwii, ncl, .\\\i.\ vellow. Undi-rKing these chromatophores is an 

 imniobilc l.ivei ol li<_;lit ri'lUxiinu piwnu'nt. 



