280 LIMB FIELD OPERATIONS 



EFFECT OF SPLITTING THE LIMB FIELD 



Surgical interference vith the limb field will often result in duplication of limbs, 

 the frequency varying with the species. Amblystoma punctatum is much more favorable than 

 la A. tigrinum. Transplants often result in duplications, due to disturbances to the limb 

 field. 



Locate the limits of the limb field on Amblystoma stage #29 and then cut away a thin 

 strip of ectoderm along the dorso-ventral axis of the field, splitting the field into two 

 semi-circles (see figure below). With a small hair loop and needles, clean out the meso- 

 derm lying in the exposed region (beneath the removed strip of ectoderm). 



From another embryo of the same age or slightly older, remove a strip of mid-dorsal 

 ectoderm with underlying neural tube material, trimming the strip down until it will fit 

 into the excavated region of the limb field. See that all loose mesoderm is removed, and 

 then place this strip of ectoderm (epithelial and neural) into the excavated region, hold- 

 ing it in place with a coversllp chip until it "takes" hold. Such a foreign strip of tis- 

 sue will block the Integration of the anterior and the posterior halves of the limb field. 



Similarly split the limb field into dorsal and ventral halves. Notochord with over- 

 lying ectoderm provides an efficient block, but the notochord should be taken from later 

 stages. 



BECOED OF SPLIT LIMB FIELDS 



