DEVELOPMENT OF THE EYE OF AMBLYOPSIS. 169 



The inhibition, if any, might operate through a mechanical crowding on the part 

 of a neighboring organ or the greater selective power in eliminating the food requisite 

 for the development of the eye. The first cause may be eliminated, for there is no 

 evidence whatever of crowding other than that found in normal eyes; in fact, in 

 all stages beyond the earliest, the eye is much smaller than the optic sockets can 

 easily accommodate. 



The question of selective food elimination is not so readily disposed of. The 

 ophthalmic artery provides the eyes abundantly with blood, so it is not an absence 

 of this that causes the supposed starving. Indeed if the retardation were due to a 

 lack of blood supply we would be removing the problem one step from the eye with- 

 out solving it. Besides, Loeb's experiments have shown that the action of the 

 heart may be greatly diminished without affecting the rate of growth of the larval 

 fish. The blood supply being abundant, is there any other organ that may drain it 

 of the nutriment necessary for the proper growth of the eye? Leaving aside the 

 question whether an organ can be starved by having the nutriment requisite for 

 development withdrawn from the blood by another organ, I can think of no organ 

 or set of organs that attain an unusual growth aside from the tactile organs of the 

 skin. This system of organs is undoubtedly very highly developed in the adult and 

 has also attained a remarkable degree of development at the time the fish is 10 mm. 

 long. It is, however, not unusually developed in the earlier stages before hatching 

 and shortly thereafter when the cessation of cell division, the most important 

 element of the stunted optic development, takes place. Besides this, the tactile 

 organs of Chologaster, which possesses normal eyes, are very highly, if not so elab- 

 orately, developed as in Amblyopsis. I have experimentally determined by eliminat- 

 ing the eyes altogether that the tactile organs in Chologaster papilliferus are amply 

 developed to enable the fish to live indefinitely without the use of its eyes. The 

 same must also be true of Chologaster agassizii, which lives permanently in caves. 

 While not impossible, it seems, therefore, very improbable that the tactile organs 

 affect the development of the eyes in Amblyopsis and not in Chologaster. 1 



I know of no other organs in Amblyopsis whose development differs from that 

 of Chologaster in a degree sufficient to make it a successful contestant for a food 

 supply in Amblyopsis and not in Chologaster. 



What has been said concerning organs whose presence might affect the develop- 

 ment of the eyes is equally true concerning organs whose absence might deprive the 

 eye of the necessary stimulus to reach normal development. I know of no organ, 

 either in Amblyopsis or Chologaster, whose absence in the one and presence in the 

 other might account for the difference in the degree of development reached by the 

 eyes in the two fishes. 



The conclusion is forced upon us by the above considerations that neither in the 

 environment nor in the fish itself is there a factor sufficient to account for the early 

 arrest in cell division, the retardation of the morphogenic processes, and the stopping 

 of the histogenic processes. We are therefore entirely justified in assuming that 

 the determining cause of the method of development lies in the cells themselves and 

 is inherited. The great development of the scleral cartilages beyond the needs of 



1 As an example bearing on this subject attention may be called to the tactile apparatus of the Siluridae, 

 which is certainly in many instances more elaborate than that of Amblyopsis, and yet the eyes are normal, though 

 small. 



