208 W. BALDWIN SPENCER. 



those of the external-lying cells, a prominent layer (figs. 18 



and 20, n.). 



Lacerta. 

 Two species of this genus have been examined. 



(1) Lacerta viridis, PL XVII, fig. 26. 



In this form the external indication, though recognisable, is 

 not at all prominent, consisting merely in a dark circular space 

 upon a median scale. 



The organ lies immediately beneath this within the foramen; 

 it is flattened out dorso-ventrally and embedded in deep pig- 

 ment, as represented in fig. 26, where it is drawn as a solid 

 object. Its smallness and the great deposition of pigment 

 rendered it very difficult to examine the structure in detail, 

 and the backward extension of the pigment towards the epi- 

 physis made it also difficult to distinguish any pineal stalk, 

 though in parts there were indications of its existence {Ep.^ ?) ; 

 this pigment may, however, be a deposition in the brain mem- 

 branes which must once have surrounded the stalk connecting 

 the vesicle with the epiphysis, and which persist after the 

 separation of the two has taken place. 



(2) Lacerta ocellata, PI. XVIII, figs. 27, 28, and 30. 



In this the external indication of the organ is far more con- 

 spicuous than in L. viridis; the scale with its dark central 

 circular space, surrounded by a slightly raised light-coloured 

 rim, forming a well-marked feature on the dorsal surface of the 

 head. 



Position of the Eye. — This difi'ers somewhat from that of 

 other forms inasmuch as it lies closer to the external surface ; 

 the connective tissue in which it lies completely fills up the 

 foramen, and when the brain, together with its membranes, are 

 pulled away internally from the skull, the eye is brought away 

 with them (PI. XVIII, fig. 28). The position within the 

 foramen is represented in fig. 27, where the eye is drawn as a 

 solid object surrounded by a great number of branched pig- 

 ment cells. The foramen is supposed to be cut in half longitu- 

 dinally aud vertically, one side being removed to show the 



