2U6 



EXTIRPATION OF ORGAN ANLAGEN 



THE EXTERNAL GILLS 



Select Anuran emtryos at stage #1? or #l8 or Amtlystoma embiyos (any species) at 

 stage #25 or #26 and locate the gill swellings. If avail- 

 able study Anura stage #23 and Amblystoma stage #U0 to 

 see the position of the filamentous external gills which 

 normally develop from the anlagen. 



Since all three germ layers contribute to the forma- 

 tion of the external gills, it will be necessary to extir- 

 pate an adequate area of the ectoderm and a considerable 

 amount of the underlying mesoderm of these early stages 

 in order to make the operation complete. This may be done 

 with glass needles, and deep excavation by means of a hair 



loop. Ihe phaiyngael cavity should be exposed. The gill position of the balancer an- 

 anlage on the right side may be removed and the lett siae ^^^^ (stippled) and posterior 

 left untouched for control comparison. to it the gill swelling: 



AraDlystoraa stage #28. 



Sketch (photograph) Immediately 

 after extirpation 



Sketches (photographs) of 

 subsequent development 



