EXTIRPATION OF ORGAN ANLAGEN 



2k9 



THE HEART ANLAGE 



The partial or even the complete extirpation of the heart forming mesoderm of Ambly- 

 stoma ia generally followed hy regeneration, which may mean the entire heart. The heart 

 field extends well teyond the limits of the ultimate heart forming area so that even the 

 extirpation of an area equivalent only to the ultimate heart may result in the formation 

 of a small heart or hearts. With these facts in mind, derived from the work of Copenhaver, 

 attempt to extirpate parts of the heart as follows: 



Amblystoma stage #15 or Anuran stage #1*+ should be used, for the heart mesoderm is 

 derived from two separate lateral primordla representing the free ventral margins of the 



two hypomeres. These fuse in the mid-line, ventral to the pharynx 

 and Just posterior to the thyroid anlage to give rise to a single 

 tubular heart. The two prlmordia meet ventrally at about stage 

 #27 in the Urodeles and about stage #1? in the Anura . 



Eemove the membranes and orient the medullary plate stage with 

 the right ventro-lateral aide uppermost, in a depression in agar 

 or Permoplast. The excision and healing should be in lO'jt Standard 

 Solution. With sharp needles outline the heart area on the right 

 side of the mid-ventral line and cut out a rectangular area deep 

 enougn to include all three germ layers (see figure). It may be 

 necessary to excavate cells with a hair loop, and this should be 

 done extensively on the right side. Keep the embryo in 10^ Stan- 

 dard Solution until the wound is healed over and then gradually 

 return to full strength Standard Solution. 



Medullary plate stage 

 of an amphibian embryo 

 showing the presumptive 

 heart area to be extir- 

 pated (stippled) . 



Urodele embryos may be allowed to develop as long as possible because the heart 

 development can be viewed through the thin covering ventral epidermis. The Anuran embryos 

 should be dissected, or fixed, stained, and sectioned within about a week following the 

 operation to determine the extent of damage or recovery of the above extirpation. (See 

 section on Heart Field Operations.) 



Sketch (photograph) immediately 

 after extirpation 



Sketches (photographs) or 

 subsequent development 



