506 



HEART F lELD OPERATIONS 



Place the embryo in a Permoplaat depreaalon in such a position that the ventral heart 

 forming areas faces upward. Locate the exact position of the future heart and with sharp 

 glass needles make an incision posterior to the region of the thyroid anlage' and deep 

 enough to reach the grayish endoderm of the pharyngeal floor. Carry this incision pos- 

 teriorly to the position of the liver anlage. With a fine hair loop clean out the loose 

 cells in the mid-ventral line, forming a channel. Leave the lateral mesenchyme intact. 



NORMAL DEVELOPMENT OF HEART 



PHARYNGEAL ENDOCERM 

 , ENOOCAROtUM 



PERICARDIAL CAVITY 



CONUS ARTERIOSUS 



VENTRICLE 

 SINUS VENOSUS 

 ■VITELLINE VEIN 



TUBULAR HEART 



FRONTAL VIEW OF EARLf HEART 



BU3CKING TISSUE 



POINT OF INSERTION OF 

 BLOCK OF INERT TISSUE 



BLOCKING TISSUE 



PARTIAL DUPUCATION OF HEART COMPLETE DUPLICATION OF HEART 



REDRWN FROM EKMAN '25 



EXPERIMENTAL DUPUCATION OF HEART 



From a second embryo of the same species but of a later stage of development, remove 

 a strip of notochord long enough to fill the excavated channel. Insert it into the 

 operated embryo between the lateral heart rudiments, replace the ventral ectoderm, and 

 hold the flap of ectoderm in position for 20 to 50 minutes by means of a Briicke or lens 

 paper bridge. Alternative procedures may include flank ectoderm with underlying somite 

 mesoderm Instead of notochord. Heturn the embryo to the normal culture medium after the 

 wound has healed over. 



Should the above procedure fail to produce a double-hearted embryo, proceed with a 

 more extensive operation on an embryo one stage younger. Remove the ecto-mesoderm by mak- 

 ing a longitudinal slit from a position between the suckers posteriorly about I/5 of the 

 length of the embryo. Garry the cut doraally on one side of the embryo to the ventral 

 limits of the closed medullary fold, then forward, to complete a trapezoid. Avoid as much 

 of the head ectoderm as possible. After outlining this area, carry the incision deeper 

 until all mesoderm on the side of the operation is circumscribed. Eemove this large mass 

 of ecto-mesoderm. Prom a slightly older embryo outline and remove an area of similar 

 shape, and including ecto- and mesoderm, but from the presiimptive hind-limb region. Trans- 

 plant this mass to the operated (host) embryo wound area, hold it in place for }0 minutes 

 or more, and when healed, return the embryo to normal culture medium. (See Ekman, I925.) 



TRANSPLANTATION OF HEART FORMING AREAS 



a. Early stages ; In Anuran stage #17 or Urodele stage #25, the heart forming 

 mesenchyme from the bilateral sides has fused ventrally. Bemove a rectangular piece of 

 ventral ectoderm along with all available adherent and underlying mesoderm, and transplant 

 it as one piece to the flank region of a second embryo, previously prepared. The second 

 (host) embryo should be slightly younger than the donor. Such a transplanted heart anlage 

 should give rise to a tubular heart of four typical parts, with its own pulsations but 

 without any circulatory elements. 



