GROWTH OF AMPHIBIA AFTER THYROIDECTOMY 3 



TECHNIQUE 



The best larval (or embryonic) stage for a study of this kind 

 is that just preceding the beginning of the circulation of the 

 blood, as at this time hemorrhage is avoided and the chance of 

 regeneration of the removed tissue is less than if younger stages 

 are used. The R. sylvatica larvae at the time of operation were 

 5 to 8 mm. in length and the Amblystoma larvae were 10 mm. 

 in length. The animals were anesthetized and were operated 

 upon in chlorotone as recommended by Harrison ('04). The 

 solution used was 0.02 per cent chlorotone in 0.3 per cent sodium 

 chloride. 



A layer of paraffin blackened with carbon was put into a 

 Syracuse watch-glass and in it were made six grooves, each 

 sufficiently wide to admit an embryo lying ventral side up. 

 After the thyroid gland was removed the embryo was left in 

 position for about an hour or until five other operations had 

 been performed, the first then being removed to make room for 

 the seventh. By that time the wound had sufficiently healed 

 to permit handling with a pipette. Asepsis was found to be 

 unneccessary. 



The operations were performed under a binocular microscope. 

 A transverse incision was made with fine scissors through the 

 ectoderm posterior to the oral plate, the flap of ectoderm covering 

 the thyroid anlage was pulled caudally, the mesenchyma pushed 

 laterally or removed, and the exposed anlage of the thyroid was 

 removed together with that portion of the ventral wall of the 

 pharynx surrounding its proximal margin. The thyroid being 

 opaque is readily distinguished from the translucent mesenchyma. 

 Care must be taken to avoid injury to the pericardium and heart. 

 Usually the wound appeared to be healed in two or three hours. 

 After the operation (one to two hours) the salt solution was 

 gradually diluted with tap-water. It was found that the em- 

 bryos were harmed by being left too long in the saline. Many 

 sylvatica larvae were kept together in the same aquarium, but 

 the Amblystoma larvae were isolated to prevent their eating 

 one another's gills. 



