184 Miscellaneous. 



therefore situated at the actual origin of these nerves. We can 

 determine their seat by experiment. By inflicting localized injuries, 

 either with red-hot iron or the scalpel, I have arrived at the following 

 results : — 



Suh-cesophageal centres. — The destruction of the median sub- 

 oesophageal lobe causes the paralysis of the chromatophores on the 

 entire surface of the body, which remains absolutely pale. If the 

 injury has only affected one side the paralysis likewise takes place 

 on one side only, but on that opposite to the injury. There is 

 therefore a manifest crossinr/ of the nervous fibres in the thickness 

 of the ganglion. 



Siq)ra-(€Sop7iar/eal centres. — The removal of the cerebral calotte 

 has no effect on the action of the chromatophores, provided that the 

 injury does not extend to the optic nerves. If, on the other hand, 

 the red-hot needle has reached the level of the optic nerve, it pro- 

 duces, simultaneously with the dilatation of the pupil, the paralysis of 

 the chromatophores of the injured side. It therefore appears that 

 the chromatophores are under the influence of two centres, one for 

 direct effects, the other for those which take place on the opposite 

 side. After the destruction of the former it often happens that the 

 chromatophores of the opposite side remain in a state of permanent 

 dilatation. Now we know that in the normal condition the sensation 

 in the Cephalopods may be expressed by the dilatation of the chroma- 

 tophores and the intensely black coloration of the skin, or else by 

 their maximum contraction and an extreme pallor. Are these two 

 phenomena regulated by two difterent centres, a chromato-dilator 

 and a chromato-constrictor ? I have not succeeded in completely 

 elucidating this point by experiments. 



Excitability of the centres. — This is demonstrated by direct stimu- 

 lation. AVe can also operate upon it and modify it by physiological 

 means : thus, it rapidly disappears after copious hcemorrhage, and 

 insensibly diminishes in animals enfeebled by starvation and a sojourn 

 in the aijuarium. It increases under the influence of certain poisons. 

 Strychnine and curari act upon it in a characteristic fashion : at 

 each convulsive shock the chromatophores behave like the muscle : 

 their expanding movement commences and ceases simultaneously 

 ■with the muscular shock. 



Form and characteristics of the movement. — The movement of the 

 chromatophore is divisible into twostages : — (1) expansion, (2) con- 

 traction. In an enfeebled animal the ditFerencc of daration between 

 the two stages is so accentuated that we can register it in an indirect 

 fashion, and in this way, by a special arrangement, I have obtained 

 outlines which are as approximate as possible. If we compare these 

 outlines with those of the contraction of the muscles of the mantle 

 we find a striking resemblance. 



The radial fibres are muscles. — Of all the characters which have 

 just been enumerated there is not one which cannot be referred to 

 the properties of rapidly contractile muscles; it is, moreover. nec^'S- 

 sary to eliminate from henceforth the slowly contractile muscles of 

 the skin. The peristaltic movements which are centred in the latter 



