TIII: OBOAM Of 1111: 01 435 



projects into the cavity of the vesicle. In the posterior portion the 



epithelial < 11s are separatd into dill', i-. nt lay. rs. the innermost of 

 which is distinguished by the abundance of its pigment. Between 

 the pigment i d e. 11s there are imbedded oth.-rs which .an be compared 

 to the r<xls of tho visual c.-lU in the | eg of Vertebrates, 



and which appear to U- in i-i>nnoction below with nerve- fibres. 



Those investigators who, like RABL-Ri < KIIAKI>, AHUIOBN, 

 Si i ACER, and others, have studied the pineal gland, ar> of opinion 

 that the jn'nt'>it tun?'/ must In- ciinsidered aa an ' eye, 



whicJi In many classes, for example in Reptiles, "/////* to be toln 

 reserved, but in most Vertebrates is in process of degeneru ' 



That we have to do in Reptiles with an organ which i art- u 

 the influence of light, does not appear improbable, when one t 

 into consideration that, owing to the tran-i t' the dermal 



scutes at the place in the skull where the parietal foramen i> 

 located, rays of light are here able to penetrate through the integu- 

 ment. The presence of a lens-like body and pigment is 

 favorable to this view. But whether the organ serves for sight, 

 or only for the transmission of sensations of warmth, whe- 

 consequently, it is more an organ for the perception of \ han 



an eye, must for the n main undecided. It Is still more 



an open question whether this organ of warmth is a strn. 

 which has In -. n developed as a special modification of the ej.ipi 

 of Reptiles alone, as the auditory sac, for example, has i 

 developed in the tail of the (.YuM.-ici.-aii My>i>, or win . ther it 

 represents a structure originally common to all Vertebrates. In the 

 latter case proccs.- generation must be assumed to be wide- 



id, for up to the present time nothing like the condition in 

 Reptiles has been found in other Vertebrates. 



In Birds and Mum amis the pineal process undergoes metamor- 

 phoses which give rise to an ore/a dar structure. 



In Birds (fig. 246) it never attains such great length as in 



liians and Reptihs. At a certain stage it sends out fro i: 

 surface into the surrounding vascular coniuv c. llular out- 



growths, which increase in number by means of budding and finally 

 break up into numerous small follicles (tig. 24G/). These consist of 

 several layers of cells, the outermost being small, spherical elements, 

 the innermost cylindrical ciliated cells. The proximal portion of the 

 pint al process does not become involvtd in the foilieular metamor- 

 phosis and persists as a funnel-shaped outfolding of the roof of the 

 between-brain ; the individual foilieular vesicles constricted off from 



