692 



Regeneration 



liead connective tissue, auditory vesicle, or 

 any other region unless the retina is present. 

 If the retina with iris is transplanted and 

 rounds up to form a vesicle, the lens regen- 

 erates. 



Sato ('30, '33) showed that there is a 

 gradient of material in the iris. Sato divided 



lens capsule is left behind. In rabbits (Ran- 

 dolph, '00), complete regeneration may occur 

 after injury, but here the regeneration is 

 from old lens epithelium, not from the bor- 

 der of the iris. 



Within recent years studies have appeared 

 (Harrison '29, '33; Twitty, '34; Twitty and 



Fig. 245. Reconstitution of the eye in Triturus taeniatus. A, Before the operation; B-F, after 2, 14, 21, 

 28 and 49 days. (From H. Wachs, '14.) 



the iris into six parts with definite locali- 

 zation of potency. Beckwith ('27) had shown 

 that if the eye is rotated early the choroid 

 fissvu"e develops ventrally. Sato turned it in 

 later stages and the choroid fissure retains 

 its rotated position. In this case the lens 

 regenerates from the ventral margin of the 

 iris opposite to the choroid fissure. If the 

 lens is removed early and replaced by in- 

 different ectoderm, the eye may never have 

 a lens, in which case the vitreous humor 

 may be both incomplete and imperfect. 



The majority of these experiments have 

 been performed upon amphibians. The ex- 

 periments have at one time or another been 

 duplicated on teleosts, lizards and other 

 forms. The removal of an opaque lens is a 

 frequent operation, but in the mammals the 



Schwind, '31; Stone, '30) in which, by 

 heteroplastic transplantation, the effects of 

 the graft upon the host and the host upon 

 the graft have been studied. In general these 

 studies give a mass of evidence to show that 

 ultimately the eye tends to regulate to an 

 average condition; a large eye on a small 

 host tends to conform to its surroundings — 

 it is larger than the eye removed to the host 

 but smaller than it would have been upon 

 the donor. 



Reports by Schotte ('38) and his co- 

 workers show that lens may be formed from 

 tissues foreign to the eye. The chief outlook 

 of this work has been not the regeneration 

 of the lens but the transformation of other 

 tissues into lens. This links the eye to the 

 problem of determination. It likewise adds 



