Miscellaneous. 1 83 



On the Nature of the Movement of the Chromatophores of 

 Cephalopods. By M. C. PnxsAiix. 



It is stated by P. Bert, in his important memoir on the physiology 

 of the cuttle, that the movement of tlie chromatophores is due to 

 dilatatory muscles with rapid contractile power. MM. Pelvet and 

 Prodorick were the tirsfc to support this view with experiments. 

 Another theory, whicli owes its origin to anatomical observations, 

 considers tlicse movements to be of an amoeboid nature. It was 

 advanced hj Harting, and has been maintained by MM. Raphael 

 Blanchard, P. (jiirod, and quite recently by M, Joubin. However, 

 the latter author reconciled the theories by admitting the former for 

 the young and the latter for the adult chromatophore, and, as a 

 corollary, the transformation of muscular into connective Jibj-es. 



The theory of P. Bert is the only rational one. It was to demon- 

 strate the justice of it that I undertook a series of investigations at 

 the zoological station of Arcachon, where, thanks to MM. Viallanes 

 and Jolyet, I found the material necessary for my task. 



Three kinds of movements are distinguishable in the chromato- 

 phores. 



1. Tremulous movements. — In a living Cephalopod, in a state of 

 rest, the chromatophores are constantly agitated by little shocks, 

 which are scarcely visible ; it is Like an incessant and rapid 

 trembling, and this gives the skin of Cephalopods its characteristic 

 appearance. These movements are under the control of the nervous 

 system ; they disappear as soon as the pallial nerve is divided or the 

 chromato-motor centres are injured. In that case the chromato- 

 phores diminish still further in diameter and the skin attains its 

 maximum degree of paleness. 



2. Undulating movements. — These do not set in, as a general rule, 

 until after death. They consist in the maximum expansion followed 

 by the contraction of the chromatophores. Their characteristic 

 feature is that they commence at one or several points and radiate 

 thence in all directions, to reproduce themselves in an irregular and 

 disordered fashion. They are due to the direct stimulation of the 

 skin, and persist for a long time after death. 



3. Movements of functional activity. — These occur in the living 

 animal only, and servo it as a means of defence. They are the result 

 of reflex actions, which depend entirely on the central nervous 

 system. Accordingly the section of the pallial nerve at the neck 

 suffices to render them impossible in the portion of the body inner- 

 vated by this nerve. The galvanization of the peripheral extremity 

 of this nerve provokes the dilatation of the chromatophores, which 

 remain in a state of expansion so long as the stimulus continues. 

 It is a veritable tetanization. It is produced and ceases simidta- 

 neously with that of the muscles of the mantle. A single stimulus 

 induces a transitory dilatation, which appears and terminates simidta- 

 neously with the muscular shock. 



Chromato-motor nen'ous centres. — If we stimulate the central 

 extremity of the pallial nerve we obtain the dilatation of the chroma- 

 tophores of the opposite side. The centre of the reflex actions is 



