24 Professor W. Baldwin Silencer [Jan. 28, 



there is no special external indication, nor, on the other hand, does 

 the presence of the latter indicate infallibly a well-developed eye. 



Thus in Hatteria, the New Zealand lizard, there is no external 

 indication of the eye, save perhaps a slight absence of pigment in the 

 skin immediately above the parietal foramen ; but if longitudinal 

 vertical sections be cut through the head, the eye is found lying 

 deeply embedded in connective tissue within the foramen. It has 

 the form somewhat of a cone, whose base is directed forwards and 

 upwards, whilst the apex points backwards and is united with the 

 pineal stalk. The base of the cone is formed by the lens, which 

 consists of elongate, nucleated cells, arranged so as to form a cone 

 whose apex points inwards and lies in the line of the optic axis ; the 

 lens is directly continuous with the retina, and thus, unlike that of the 

 paired eyes, is formed directly out of what was originally part of the 

 brain- wall. The retina itself is well developed in Hatteria, and forms 

 a strong contrast to that of the lateral eyes, inasmuch as the rods, em- 

 bedded in dark-brown i3igment, face inwards and line the cavity of 

 the vesicle, whilst in the paired eye, the same structures are on the 

 side of the retina remote from the cavity of the eye in the adult, 

 though this, it must be remembered, is not homologous with the 

 cavity in the pineal eye. External to the rods lies first a layer 

 of spherical, nucleated elements, then a molecular layer consisting 

 of finely punctated material, then another layer of spherical elements, 

 followed by a layer of cone and spindle-shaped structures, which 

 again lie clirectly upon a thin layer of nerve-fibres spreading out 

 from the pineal stalk. The rods lying in the optic axis are much 

 elongated and very prominent, a feature common to all eyes which 

 are still in connection with the optic stalk. This may be taken as 

 a description of the retina of a typical j)ineal eye, though it is more 

 highly developed in Hatteria than in many other lizards at the 

 present day. The remainder of the ejiij^hysis may be divided into 

 two parts, a solid pineal stalk nearest the eye, and a hollow part 

 running back to the roof of the brain and overlying, as it nears the 

 latter, the vascular roof of the third ventricle. 



In many lizards degeneration seems to have set in and the eye 

 to have become more rudimentary than it is in Hatteria ; in fact, in 

 the latter, the only sign of its rudimentary nature is its position 

 deeply buried in the connective tissue within the parietal foramen, 

 a position which must prevent its functioning as an organ of vision 

 at the present time. If we take such a lizard as Varanus hengalensis, 

 sections through the parietal foramen show that the eye is well 

 developed and placed not far below the surface of the head, whilst 

 between it and the latter is a marked absence of the pigment cells 

 which form so prominent a feature in sections of the skin all around. 

 Further examination however reveals an important point of difference 

 when compared with Hatteria — the eye has lost its connection with the 

 proximal part of the cprphijsis, which has the form of a hollow process 



