638 Dynamic Theory. 



of a cornea, but beneath it is an accumulation of pigment which makes 

 it inoperative. In Hatteria the eye appears good, but it is covered by a 

 thick band of tissue which makes it useless. In both these animals the 



rods and cones are developed extraordinarily in some parts. 

 t 



FIG. 351. Pineal Eye-Scale of small Lizzard, Calotis. 



C. -Transparent Cornea in the middle, with Eye beneath. 



1 In fishes the conarium is commonly only a 

 vasculo-membranous, pyramidal sac continued 

 from the third ventricle, the base expanding 

 from the anterior space between the optic lobes, 

 and the apex directed forward and attached to 

 the roof of the cranium. In some fishes there 

 is medullary matter in the conarium, in some 

 there is gray matter. In lepidosiren, sturgeon 

 and shark it is membranous only. In all it has 

 an abundance of vessels. 



In modern amphibians this eye is joined to the pineal gland during 

 embryonic life, but is separated in the adult. The eye is greatly de- 

 generated, and of course f unctionless. Among the fossil labyrintho- 

 donts this pineal eye was outside the skull, and connected with the skull 



,L 



FIG. 351. 



""^"" i! " SSs *i^ 



FIG. 352. 



FIG. 352. Diagram of vertical section through the Brain and Pineal Eye of a Liz- 

 zard (Lacerta Viridis). 



Pa. Parietal bone. O. Optic Lobes. 



C. Cuticle. CH. Cerebral Hemispheres. 



Ep. Epidermis. G. Pineal Gland. 



.fifRete mucosum, pigment layer. N~o. Nerve leading to the PinealEye. 



Pig. Pigment. L. Lens of the Eye. 



by powerful muscles. f ' The pineal eye was pre-eminently a sense or-^ 

 gan of pretertiary periods ; it has probably never been functional since 

 these remote ages, and yet its rudiments persist in every human brain. 

 Moreover, these eyes are of the invertebrate type, pointing back to that 

 conjectural molluscoid ancestor which was 'transparent and had a me- 

 dian eye.'" 2 In the invertebrate eye (as shown elsewhere) the optic 

 nerve does not pass through the retina and then spread over its anterior 

 surface, but spreads itself over the back side of the retina, leaving it 



1 Hatteria is same as "Rhynchocephalus," a New Zealand Gecko. Varan us is a mon- 

 itor. The pineal gland is a connection and derivative of the mesencephalon. That and 

 the pituitary gland are vertical expansions of the third ventricle. 



2 Mrs. Bodingtonin Pop. Sci. Mo., Oct. 1888. Also Lubbock Senses and Instincts of An- 

 imals, p. 127. 



