166 W. BALDWIN SPENCER. 



schilder 4 ; selten nur 3 ; die beiden mittelsten hintereinander 

 stehenden, die kleinsten, das obere, grossere regelmassig 

 5-eckig, meist mitten, mit einer runden, vertieften stelle/' and 

 he adds in a foot-note, " Eine eigne Driisenstelle bezeichnend/' 

 The external marking on the surface of the head is not repre- 

 sented in the drawing of L. agilis (fig. a, Tf. xix), but his 

 description shows that he recognised the presence of an internal 

 modification corresponding to the specialised scale. 



Milne Edwards^ and Duges^ both figure the external modi- 

 fication in certain lizards, but neither, strangely, make the 

 slightest mention of it in their descriptions of the animals. 



Leydig,^ writing more than forty years later, is apparently 

 the first to point out with any clearness the presence of the 

 organ, and to give some account of its structure and of the 

 development of the epiphysis, though he entirely failed to dis- 

 cover the relationship existing between the two. Under a 

 high power, he says, the body in question which lies " above 

 the thalamencephalon or the region of the third ventricle," is 

 seen to consist of long cells similar to those of a cylindrical 

 epithelium, so arranged that they form altogether a shallow pit 

 with a circular outline ; the rim of the pit is turned upward, 

 and has a thick black girdle of pigment ; " welcher schon fiir 

 das freie Auge das Organ sehr bemerklich macht.^' After stating 

 that it has a special blood supply, he goes on to say : " Das 

 Organ ist keineswegs, woran Man zunachst denken konnte, 

 die embryonale Zirbel, dem diese folgt erst darunter und ist 

 von ganz anderer Beschafifenheit." 



" Fragliches Gebilde entspricht ferner der Stelle, wo sich am 

 skeletirten Schadel des fertigen Thieres im spateren scheitel- 

 beine, das oben schon erwahnte kreis runde Loch befindet." 



He examined the organ in Lacerta agilis, L. muralis, 

 L. vivipara, and Anguis fragilis. On pi. xii (fig. 159) he 



* " Recherches Zoologiques pour servir a I'histoire des Lezards," ' An. Sci. 

 Nat.,' 1829, torn, xvi, p. 50. 



2 " Memoire sur les especes iudigenes du genre Lacerta," ' An. Sci. Nat.,' 

 1829, torn, xvi, p. 337. 



3 * Die Arten der Saurier,' 1872, p. 72, Taf. 12. 



