THE PINEAL GLAND 301 



thalamencephalon, situated a little to the left side of the middle 

 line (fig. 4, a). At the next stage (fig. 4, b) we find the usual two 

 pineal organs as seen in embryo Lacertilia: one placed a little in 

 front of the other, and the cavities of the two perhaps still 

 communicating with one another, while the cavity of the 

 posterior also communicates with that of the brain. It is 

 important to notice, however, that the more anterior of the 

 two does not lie entirely in front of the more posterior, but 

 partially overlaps it on the left side, as shown in figs. 3 b and 4 b. 

 I had arrived at this result, and actually sent my manuscript and 

 drawings to England for publication, before I was aware that 

 Charles Hill, in America, had obtained a precisely similar result 

 in the case of bony fishes (compare a and b, fig. 3). I think the 

 fact of these two results having been arrived at quite indepen- 

 dently is of great importance in estimating their true value. 

 In bony fishes, however, as we have already seen, it is the right 

 pineal organ which persists in the adult ; and though it never 

 gives rise to an eye-like structure in this group, it is doubtless 

 homologous with the right (posterior) pineal sense-organ of the 

 lampreys. In Sphcnodon, on the other hand, the left (anterior) 

 pineal organ of the embryo becomes the remarkably well- 

 developed " pineal eye " of the adult. It separates completely 

 from its fellow, and its upper wall very soon becomes thickened 

 and lens-like, while its lower wall becomes deeply pigmented 

 and gives rise to the "retina" (fig. 4, c). Although at first 

 distinctly on the left side, it soon becomes median in position, 

 and at the same time becomes widely separated from the brain, 

 occupying the well-developed parietal foramen in the roof of the 

 skull. The other pineal outgrowth, or so-called " stalk" (Ep. 2), 

 appears to occupy a median position from the first ; nevertheless 

 it probably represents the right-hand member of an original 

 pair. Its development differs widely from that of its fellow. 

 It becomes greatly elongated and finger-shaped, and curves 

 forwards over the roof of the thalamencephalon towards the 

 pineal eye, which lies a little in front of and above its apex. 

 Its cavity for a long time continues in free communication with 

 that of the brain at the point of origin, between the closely 

 approximated superior and posterior commissures. The nerve 

 of the pineal eye appears as a band of fibres running from the 

 retina beneath this so-called "stalk"; but its connection with 

 the brain-roof has unfortunately not yet been made out. From 



