THE PERCEPTION OF FORM 



645 



mechanism is lacking (Fig. 771). In the lamprey the cornealis muscle ^ 

 which lies outside the orbit and is inserted into the dermal part of the 

 cornea, draws the cornea taut as it contracts, flattens it and thus presses 

 the lens, which lies in contact with this tissue, backwards to approach 

 the retina. It may be that a contraction of the extra-ocular muscles 



Figs. 772 to 776. — Accommodation in Teleosts. 



Fig. 



772. — A cliange in position of the lens ; in relaxation for near, n, and 

 in accommodation for distance vision, d. 



Fig. 773. Fig. 774. 



Figs. 773 and 774. — The left eye of the sea-bass, Serranus cabriUa (after Beer). 



Showing the aphakic area in the pupil in which can be seen the inverted 

 retinal image of a gas flame situated in the temporal jDai't of the eye. Fig. 773, 

 at rest ; Fig. 774, in active accommodation. 



Fig. 



Fig. 776. 



Figs. 77") and 776. — The left eye of the Ijlenny, Bhnniiis sanguinolentis 



(after Beer). 



Fig. 775, at rest ; Fig. 776, in active accommodation (seen from above 

 the fish). 



which jacket the globe has the opposite effect of elongating it to aid the 

 relaxation of accommodation ; but this is conjectural. The spherical 

 lens, wedged between the cornea in front, the relatively solid vitreous 

 behind and the immol;)ile iris at the sides, has no suspensory apparatus. 

 This mechanism of accommodation is both simple and effective, 



1 p. 271. 



