PRODUCTION OF DOUBLE EMBRYOS 



195 



it is best to anchor one end of the loop in the nearby Permoplast, leaving but a 

 single loose end to tighten as the egg is held in position by forceps. It may also 

 help to build up the Permoplast about the egg to hold it the better. When secure, 

 use watchmaker's forceps and tighten the loop so that it constricts the 2-cell 

 stage between the blastomeres, through the jelly capsule and all. It may be 

 necessary to re-orient the egg after the hair loop has attained a grip on the 



le blastomeres can be separated without rupturing the fertilization 



lembrane. 



Constriction of on amphibian egg, within 

 its jelly capsule, at the beginning of the 

 2-cell stage, by means of Q hair loop. 

 When blastomeres are separated, two em- 

 bryos develop; when the furrow is merely 

 deepened, double embryos result. 



The loop should hold as a result of friction and the egg can be removed to an 

 appropriate #2 Stender for continued development and observation. However, 

 very fine hair or individual fibers of silk can sometimes be looped twice, re- 

 sulting in ever better (friction) holding. The degree of constriction can be con- 

 trolled with practice. 



A second method but one which aims at complete separation of the blastomeres 

 is to remove the jelly capsule and separate the blastomeres (through the fertili- 

 zation membrane) by means of a cutting movement of the side of a glass needle. 

 This can be done without rupture of the membrane. Controls for this consist 

 simply of eggs deprived of their jelly. 



OBSERVATIONS AND TABULATION OF DATA: 



1. Make sketches of any changes in the superficial pigmentation of the inverted eggs, as 

 compared with the controls. Determine whether these changes are carried over to 

 the period of gastrulation. Sketch at periodic intervals. 



2. During neurulation it should be possible to select those embryos which will, in all 

 probability, develop into double monsters. Keep accurate and periodic records of 

 developmental changes in specific eggs of this category. It is most important that 

 any sequence of sketches represent the changes in a single egg. 



REFERENCES 



FANKHAUSER, G. , 1948 - "The organization of the amphibian egg during fertilization and cleavage. " Ann. N. Y. Acad. Sci. 

 49:684. 



HADORN, E. , 1937 - "Die entwicklungsphysiologische Auswirkung der disharmonischen Kern-Plasma -Kombination beim Bastard- 

 Merogon Triton palmatus X T. cristatus. " Arch. f. Ent. mech. 136:400. 



HARVEY, E. B. , 1940 - "A new method of producing twins, triplets, and quadruplets in Arbacia punctulata, and their develop- 

 ment. " Biol. Bull. 78:202. 



