250 EXTIRPATION Of ORGAN ANLAGEN 



THE BRAIN 



Amblyatonia punctatum (or tigrinum) embryos should be freed from their Jelly membranes 

 at stage flh to #l6 and allowed to grow at about l8°C. In Urodele Growing Medium until 

 they reach stage #52- At this time the primary brain vesicles have been developed and can 

 be outlined from the exterior of the embryo. 



Embryos of this stage show some movement and can be quieted in 1/5OOO M.S. 222 fresh- 

 ly made up in Growing Medium. When fully narcotized, transfer to a Syracuse dish with 

 bottom of soft paraffin or Permoplast and filled with Growing Medium saturated with sodium 

 sulfadiazine. With a sharp scalpel make a single cut Just anterior to the gill anlagen 

 and the first somite, Just posterior to the auditory vesicle. The head will be removed by 

 such a cut, but particularly the entire brain. A sharp scalpel will bring the cut surfaces 

 together and within l8-2l+ hours the wound should be entirely healed over. 



The purpose of such an extirpation (or ablation) is to determine the degree of further 

 differentiation without benefit of the brain and the three seta of sense organs. (See 

 Detwiler's papers) Obviously such an embryo cannot feed so that its life spand is deter- 

 mined by the amount of yolk available. Bbwever, the anlagen in the vicinity of the cut 

 (gill and balancer fields) will be the most likely to show variations in the direction of 

 size and number of parts. Such embryos will generally show full development of the heart 

 and circulatory system; will respond to stimuli; but will be somewhat more difficult to 

 anesthetize than the controls (Anagnostis, 19^*8 unpublished). 



(Note: Extirpation of limb anlagen will be accomplished in connection with limb 

 operations. ) 



Sketch (photograph) immediately Sketches (photographs) or 

 after extirpation subsequent development 



