13 



1. The central spherical cell, which contains 

 pigment granules, is a uninucleate cell which originates 



in the epidermis and later sinks down into the dermis. 

 The cell wall is a tough elastic membrane, and the 

 pigment granules are arranged round the periphery of the 

 cell, leaving the central protoplasm clear. 



2. A girdle of about 18 mesodermal cells becomes 

 grouped round the equatorial region of the pigmented 

 cell, in a plane parallel to the epidermis. These cells 



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Fig. II. — Section of the skin. Highly magnified. 



finally become differentiated into triangular muscular 

 bands of fibrous tissue, the basal side of the triangle 

 adhering to the wall of the vesicle, and the long thin 

 apical legion being lost amid the surrounding tissue of 

 the dermis. A basal nucleus shows in each fibre. 



•'!. The elasticity of the vesicle wall opposes the 

 contractile tendency of the radial fibres. When the latter 

 contract, and the wall relaxes, the vesicle becomes 

 stretched out and flattened in a plane parallel to the 



