EXTIRPATION EXPERIMENTS ON ORGAN ANLACEN 



PUEP^E: To remove organ anlagen and to determine the ability of the embryo to adjust 

 to the loss. 



MATERIALS : 



Biological : Various stages of Amblystoma as designated for each experiment. 



Technical : Standard equipment for operating on and caring for embiyos. 



METHOD : 



Precautions : 



a. The post operative care of embryos is Important, for they are naturally suscep- 

 tible to bacterial infection. This can be reduced somewhat by operating and 

 healing in 0.1^ sodium sulphadiazine, and keeping them in cool media. 



b. Bemove only the areas and cell layers indicated, at the designated stage. Organ 

 fields become contracted with succeeding stages. 



c. Study section on "Wound Healing". 



Controls : The controls for extirpation experiments consist of the same operation but 

 without the actual removal of the organ anlage. 



Procedure : Operate in 10^ Standard Solution and transfer to full strength Standard 

 Solution when the wound is fully healed. 



THE UROCELE BALANCERS 



The balancers are slender rod-like appendages which project from the side of the head, 

 slightly posterior and ventral to the eyes, and which serve as supports to hold the head 

 off the bottom and maintain balance in many Urodeles (see Amblystoma series stage #^0). 

 They are present in most species of Triturus, in Amblystoma punctatum (maculatum) Jeffer- 

 sonlanum, mlcrostomum and opacum but are absent in A. tigrinum. The club-shaped ends of 

 the fully formed balancers are sticky, and this condition may be taken as a criterion of 

 normal development. 



Select Amblystoma punctatum or opacum at stages #28 to #52 and extirpate the balancer 

 anlage on the righL side, leaving the left side as the control. Eemove both the ectoderm 

 and the underlying mesoderm from a circular area posterior and slightly ventral to the 

 eye, on the mandibular arch. The dorsal margin of the balancer area is on a direct line 

 from the dorsal border of the eye, and the area extends to a level below that of the eye. 

 The area also extends from the posterior margin of the eye to the first gill slit. (See 

 sketch) 



Sketch (photograph) immediately Sketches (photographs) of 

 after extirpation subsequent development 



-21+5- 



