mVEKTEBRATA, CRYPTOQAMIA, MICROSCOPY, ETC. 703 



and that the protoplasmic mass in which it is imbedded goes to form 

 the cellular investment and the radial fibres. 



Physiological Experiments.- — These leave no doubt as to the in- 

 fluence of the nervous system on the chroniatophores, and are of great 

 interest. Using chiefly Eledone mcschata, the author shows that there 

 are fibres in the nerves of the arms, mouth, and funnel, which, when 

 stimulated, bring about a darkening of the integument ; these nerves 

 are connected with the pedal and visceral ganglia and with the median 

 portion of the lower half ring, which is known to be in connection 

 with the optic ganglion, and there is in this region, it is believed, a 

 special centre for the stimulation of the chromatophores ; the results 

 of section of the optic nerve and observation on the changes which 

 obtain when the animal is in the presence of difterent colours, leads to 

 the view that the chromatojihores may be stimidated, after a reflex 

 mode, by the influence of light on the eye. It is also probable that 

 changes may occur at the will of the animal, and support is aff'orded 

 to this view by the statements of Colosanti with regard to the 

 " nervous axis " of the arms of the cephalopod, which appears to have 

 the structure of a central organ ; finally, changes occur when the integu- 

 ment is stimulated, whether mechanically, chemically, or electrically. 



The author concludes with some remarks on the " mechanics " 

 of the movements of the chromatophores : here the cardinal point is 

 that when active the structures in question are expanded, and when 

 passive are contracted. The opposite condition in the chameleon and 

 certain fishes is to be correlated with the absence, in them, of the 

 system of radial fibres ; but this is not the whole difference, for in the 

 Vertebrates just mentioned the changes in coloui* may take even hours 

 to be effected, while in the fresh cephalopod they occur with extra- 

 ordinary rapidity. A further proof of the value of the radial fibres is 

 afforded by the fact that in the embryonic condition of the chromato- 

 phore the separate fibres may be seen to move ; and it may well be 

 concluded that the extension of the chromatophore is due to the con- 

 traction of all the radial fibres, which moreover always move in straigJd 

 lines and never exhibit the looped arrangement which they necessarily 

 would, if they were as some have supposed, nerve-fibres passing to the 

 contained protoplasmic mass. The subsequent contraction of the 

 chromatophore appears to be principally, though not altogether, due 

 to the elasticity of the cellular investment, and the rapidity with which 

 it is effected is well explained by the supposition that we have to do 

 with what is practically a weighted muscular fibre ; fixed at one end 

 to the skin, there is attached to its other end the movable mass of the 

 chromatophore, where the elastic force of the investment and the con- 

 tractility of the pigment body represents the weight. The author 

 expresses his belief that nerves pass to the separate radial fibres, 

 although the presence of these has not yet been demonstrated. 



There is an account of a few experiments with poisons ; no effect 

 was observed with cui-are. 



Shells of the Cephalopoda in relation to the Body of their Con- 

 structor.* — Professor Owen returns with new arguments and fresh 

 * ' Proc. Zool. Soc. London ' (1878) p. 955. 



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