83 



tissue occurring in lliis position in all the filaments. This tissue obscures the nerve 

 fibres and makes it somewhat difficult to follow out their course in the sections. The 

 sections from which the present description is taken, and one of which is represented 

 slightly diagrammatic-ally by the figure, were prepared from pieces of skin treated when 

 fresh with chloride of gold. This reagent stains the nerves black or violet, and affects 

 the remaining tissues slightly or not at all. Thus the nerves can be traced through the 

 granular tissue just mentioned. The granular tissue is somewhat opaque, consisting of 

 irregularly branched cells the contents of which are coarsely granular. These cells 

 exactly resemble in structure the chromatophores of the right or coloured side of the 

 body, but they are not coloured. In fact, to use a seeming paradox, these cells are 

 colourless chromatophores ; that is to say, they are chromatophores of which the granules 

 instead of being black or orange are white and opaque. Thus the white colour of the 

 under side of the sole is not due to the absence of chromatophores, but merely to the 

 absence of what is usually called colour in the chromatophores ; the pigment cells are 

 not absent from the skin of the lower side, but are bleached. It is a very common 

 thing to find coloured blotches on the lower side of a sole, and from the above it is 

 evident that these coloured blotches are not due to the development of chromatophores 

 in certain areas while they are absent elsewhere, but are due to the fact that the 

 chromatophores in these areas are coloured, while in the rest of the skin of the lower 

 surface they are white. 



One of the superficial epidermic sense-organs of the under side of the head is 

 represented in section in the figure. It will be seen that they do not differ in structure 

 from the sense-organs of the dermal tube of the lateral line. The sensory hairs are 

 present in these organs, though not shown in the figure, as they are not well preserved 

 by the chloride of gold method of preparation. 



M 2 



