Chap, v.] FIBROUS CONNECTIVE TISSUES. 37 



hitherto mentioned are fixed corpuscles ; they do not 

 show movement. Kiihne and Rollett ascribe to the 

 corneal corpuscles a certain amount of contractility, in- 

 asmuch as they are said to be capable of withdrawing 

 their processes on stimulation. When this ceases they 

 are said again to protrude them. According to Strieker 

 and Norris, they acquire contractility when the corneal 

 tissue is the seat of inflammatory irritation. It can 

 be shown that the connective tissue cells consist, like 

 the endothelial plates, of a ground plate and a fibrillar 

 reticulated (granular-looking) substance around the 

 nucleus, and extending beyond the ground plate into 

 the processes of the cell. _ 



42. Pigment Cells. In the lower vertebrates, 

 especially fishes, reptiles, and amphibian animals, we 

 find certain branched nucleated connective tissue cor- 

 puscles, distinguished by their size and by the proto- 

 plasm both of the cell-body and processes but not of 

 the nucleus being filled with pigment granules. The 

 pigment is either white or yellow, or more commonly 

 dark brown to black. These cells are called pigmented 

 connective tissue cells, or simply pigment cells. They 

 are very numerous in the skin of fishes, reptiles, and 

 amphibian animals, and also around and between the 

 blood-vessels of the serous membranes. They are also 

 present in man and mammals, but then they are 

 chiefly limited to the eye-ball, where they occur in the 

 proper tissue of the iris of all but albino and bright 

 blue eyes, and in the tissue of the choroid membrane. 

 In dark eyes of mammals a large number of these cells 

 are found in tire tissue between the sclerotic and 

 choroid, as the lamina fusca, and also, but to a more 

 limited degree, in the sclerotic. As a rule they appear 

 to be of various kinds: such as are flattened, large 

 plates perforated by a number of small and large holes 

 and minute clefts ; such as possess a more spindle- 

 shaped body, and long, thin, not very richlv branched 



