62 THE CONNECTIVE TISSUES, BY A. ROLLETT. 



The pigment cells of connective tissue are for the most part 

 characterised by their beautiful stellate form, and by their nu- 

 merous processes. 



In man, in whom such pigment cells occur normally only in 

 the eye, the pigment granules are of black or brown colour. The 

 substance of which they are composed, and which is termed 

 Melanin, is still but little known in regard to its chemical 

 qualities. The granules are not perfectly round, but sub- 

 cylindrical, or elongated with rounded extremities. They more 

 or less completely fill the interior of the stellate pigment cells 

 of the eye. As a general rule the ends of the cell processes 

 remain colourless. The nucleus of these cells, in some cases, 

 occupies the middle of the cell, and appears bright and dis- 

 tinctly defined ; it contains no pigment, as is also the case with 

 the cell substance which bridges over the broad side of the 

 nucleus, whilst the cell mass lying around the nucleus, and its 

 processes, are closely packed with the pigment molecules, so that 

 the position of the nucleus appears as a clear space. In the 

 stellate cells of the iris, and of the choroid of man, the pigment 

 granules are most abundant shortly after birth* Pigment 

 cells also occur in the innermost layer of the sclerotic. In many 

 animals, isolated pigment cells are thickly disseminated through- 

 out the whole thickness of the sclerotic. Movements have been 

 observed in the stellate pigment cells (chromatophores) of Am- 

 phibia, ) and Fishes. J The pigment granules sometimes appear 

 collected into round masses, and at others are diffused in the 

 cell processes, which are often prolonged to a considerable 

 distance. The movements observed are exceedingly tardy in 

 adult frogs, but in the embryoes of these Batrachians they are 

 somewhat more active . The spontaneous changes of form of 

 the pigment cells in the skin of these animals, or those which 

 are called forth by changes in the intensity of the light, are 

 connected with the phenomena of change of colour which they 



* Briicke, Anatomische Beschreibung der menschlichen Augapfeh. Berlin, 

 1846, p. 20. 



f Biiicke, Denkschriften der Wiener Akademie, Bd. iv., p. 23. 

 | Buchholtz, Reichert and Du Bois' Archw, 1863, p. 74. 

 Biisch, Miiller's Archiv, 1856, p. 425. 



