288 EYE FIELD OPERATIONS 



SELF-DIFFERENTIATION OF THE EYE ANLAGE 



Consult the exercise on "The Culturing of Isolated Amphibian Anlage" for the description 

 of the basic procedure necessary for this part of the exercise. 



Isolate and attempt to culture the same areas used in the "Defect Experiments" (above). 



The degree of self-differentiation is indicated by the degree of independent development 

 in isolation culture. This part of the exercise should inform the student as to just when 

 the lens and the vesicle (retina, etc.) are "self-differentiated". 



EYE INDUCTIONS 



This is an extremely delicate operation (Mangold, 1931) and should be attempted by only 

 those students who have proven their skill in operative procedures. " 



Gastrulae (Anura stages #10 and #12) are decapsulated. The donor (stage #12) is dis- 

 sected so as to expose the most anterior portion of the archenteric roof. This material 

 is excised in one piece and is quickly inserted through the blastocoelic roof of the younger 

 (stage #10) gastrula (see diagrams). If the normal "inductive" (see Glossary) influences 

 are exerted on the overlying ectoderm of the blastocoelic roof, accessory optic struc- 

 tures will be formed. (See exercise on "The Organizer" for procedures. ) 



TRANSPLANTATIONS 



Under this heading will be included the simpler transplantations of optic cup and/or lens 

 primordium in order to determine their interrelationship in the normal development of 

 the eye as a whole. There will also be included the homoplastic, heteroplastic, and 

 xenoplastic transplantations of larval eyes. 



LENS INDUCTION: (See Stone & Dinnean 1940 and Liedke 1942) 



1. Remove the presumptive lens ectoderm from over the optic vesicle or cup of 

 Anuran stage #16 or #17, (Urodela stages #21 to #26)* without injuring the 

 underlying structures. Quickly excise a slightly larger piece of belly ecto- 

 derm from another embryo, of the same stage previously stained with Nile 

 Blue Sulphate. Place it over the exposed optic vesicle. Gently pat it into 

 place and, if necessary, hold it in place with a Brllcke, lens paper, or piece 

 of coverslip. It should heal within 20 to 30 niinutes. (See section on "Wound 

 Healing". ) 



2. Remove the ectoderm from over the optic vesicle of Anuran stage #17 

 (Urodela stages #21 to #26)*. Prepare a host embryo (of the same stage) by 

 making a deep pit ventral to the somites at about the mid-body region, leav- 

 ing the flap of ectoderm over the pit intact. (See A-2-c under "Defect Ex- 

 periments" on the preceding page. ) Quickly cut out the optic vesicle of the 

 donor and transfer it to the excavated pit of the host. Orient the vesicle in 

 the same position as in the donor, i. e. , with the bulbous part of the vesicle 

 facing outward. Replace the ectodermal flap over the transplanted optic 

 vesicle, and hold it in place with Briicke until healed. 



These two experiments are reciprocally related. Part 1 will indicate whether foreign 

 (non-presumptive) ectoderm will respond to inductive influences from the intact optic 

 vesicle and Part 2 will indicate whether the optic vesicle, transplanted to a foreign 

 site, can there induce a lens in the overlying (foreign) ectoderm. All such embryos 

 should be allowed to progress to the external gill stage before dissection analysis. 



♦ After Urodele stage #26 (Anura stage #17) the piotential lens forming ectoderm becomes adherent to the underlying optic cup, 

 and cannot be completely removed. The older embryos can he anesthetized in MS 222. 



