326 Charles R. Stockard 



smaller than its mate. A section through the eyes of an embryo 

 of this kind when seventy-six hours old is shown in Fig. 60. The 

 left eye is decidedly smaller than the right and possesses a cor- 

 respondingly small lens. From the comparative study of a num- 

 ber of individuals it may be safely stated that this difference in 

 size between the two eyes will not be overcome later, nor on the 

 other hand will the small eye degenerate or disappear. The em- 

 bryo will hatch with its eyes in dissimilar conditions comparable 

 to the state of things shown by this seventy-six hour stage. The 

 brain is normal and two nasal plates are present. 



An embryo closely similar to the one just described was sec- 

 tioned after hatching. Its large eye appears as in Fig. 61. More 

 anterior sections show a small eye looking forward with a some- 

 what protruding lens in its cup. Behind this small eye is another 

 lens lying free in the ectoderm (shown in Fig. 61). This lens is 

 perfectly differentiated and appears to have arisen independently. 



A further reduction of the eye is shown by Fig. 62. In this 

 thirteen day embryo the left eye is perfect and the right is rep- 

 resented by a small cellular mass lying close against the brain. 

 The lens of the right side is entirely wanting. In life the head was 

 slightly one-sided, obviously on account of the asymmetrical eye 

 development; no indication of the cellular mass could be detected 

 and the embryo seemed truly one-eyed. 



A section of another seventy-six hour individual which in life 

 also seemed to be one-eyed is illustrated by Fig. 63. The brain 

 is normal and almost bilaterally symmetrical, an ordinary left 

 eye exists but there is not the trace of an indication of the right 

 optic cup. An ectodermal thickening represents the right lens 

 in process of formation in the position that it would typically 

 occupy. This lens anlage must have arisen independently of a 

 stimulus from an optic cup and is well removed from the brain, so 

 that no direct stimulus from that source can be responsible for its 

 appearance. 



Other one-eyed individuals showed complete absence of all 

 parts of the second eye, the lens as well as the optic cup failing to 

 arise. The occurrence in the Mg solutions of these one-eyed 

 embryos as well as the cyclopean embryos suggests that the chem- 



