32. PARABIOSIS AND TELOBIOSIS 



PURPOSE: To learn the technique of grafting embryos together in various positions, and 

 to study the effect of such fusion on the behavior and the morphology of paired larvae. 

 Pairs which survive metamorphosis may be studied for shared structures, and for 

 hormonal relations. 



MATERIALS: 



Biological: Anuran (stages #15 to #17) or Urodele (stages #22 to #29) larvae. 



Technical : Syracuse operating dishes with permoplast or paraffin bases. 



METHOD: 



Precautions : 



1. Moderate precautions relative to sterile conditions will prove adequate. 



2. Embryos must be held together firmly but not so that there is displacement 

 of organs or any incurred damage. The Permoplast may be built up around 

 the pair, leaving small opening above for access to the medium and respira- 

 tion. 



3. Operate in hypertonic or slightly alkaline media, or in a deficiency of Cal- 

 cium to facilitate adhesion. Gradually return the pair to normal medium. 



Controls : Operated but not fused embryos consti- 

 tute the controls, to determine whether the 

 operation alone might account for any unto- 

 ward results. For'pairs that survive meta- 

 morphosis and are to be studied for hormonal 

 relations, consult papers by Burns and by 

 Witschi for adequate controls. 



Procedure : The method consists of simply re- 

 moving the epidermis, some underlying 

 mesoderm and yolk from a limited area on 

 the mirror surfaces of two embryos of sim- 

 ilar stages of development (early tail bud is 

 the best) and bringing these injured surfaces 

 together long enough to effect permanent 

 fusion by healing. This may take as little as 

 20 minutes, or as long as 24 hours, depending 

 a great deal on the temperature and the con- 

 stituents of the mediuin. 



PARABIOSIS 



Diagram illustrating position of 

 embryos (Amblystoma stage #22) 

 being fused laterally in parabio- 

 sis, within a Permoplast depres- 

 sion. Injured surfaces healing 

 together. 



Remove several embryos of corresponding age 



from their capsules and with a wide -mouthed 



pipette transfer them to the operating Syracuse dish with a base of Permoplast or 



very soft paraffin (containing some b"oswax). Bring the two embryos together and 



estimate the size of the depression wh'ch must be moulded in the Permoplast to hold 



the two embryos closely side-by-side. Make such a depression with a ball tip. 



In the vicinity of the depression, lay the twg embryos on their sides, facing away 

 from each other. With a sterile needle, or pair of forceps, outline an oval area 

 covering the region just posterior to the gill anlage on the left side of one and the 

 right side of the other embryo. With scalpel, scissors, or forceps, excise this oval 



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