The Pineal Eye of Mordacia mordax. 105 



so constantly seen in the Lacertilia, nor in the specimen 

 examined could the outlines of cells be in any way dis- 

 tinguished owing, again, doul3tless, to the bad ^ state of 

 preservation. 



The cavity of the vesicle, as in Ahlborn's and Beard's 

 specimens, is apparently filled with fluid which coagulates 

 when preserved in spirit. 



In two points, with regard to the eye, Mordacia 

 differs from Fetromyzon as described by Beard : — 



First, although the pigment is very well developed the 

 e3'e is not placed in a deep depression of the skull, the 

 latter passing quite evenly above the epiphysis. Beard 

 points out the curious fact that in Fetromyzon, when the 

 pigment is well developed, the depression is deep; when 

 absent, the depression is almost or entirely absent. 



Secondly, the pigment in the skin (pig.) passes straight 

 over the eye which would render it difficult and, when added 

 to the layer of muscle and skeleton above the epiphysis, 

 practically impossible for rays of light to reach the structure. 

 In Petromyzon, Beard states that the pigment in the skin 

 is absent above the eye. 



There can be little doubt that here, as I believe, in all 

 other animals in which it is now found, the Pineal eye 

 must, as an organ for the perception of ra3^s of light, be 

 regarded as rudimentary and functionless. 



