256 EXTIRPATION OF ORGAN ANLAGEN 



Embryos of this stage show some movement and can be quieted in 1/3000 M.S. 222 

 freshly 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 re- 

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

 cut surfaces together and within 18-24 hours the wound should be entirely healed over. 



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

 ferentiation without benefit of the brain and the three sets of sense organs. (See Detwiler's 

 papers) Obviously such an embryo cannot feed so that its life span is determined by the 

 amount of yolk available. However, the anlagen in the vicinity of the cut (gill and bal- 

 ancer 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 the controls (Anagnostis, 1948 unpublished). 



(Note: Extirpation of linnb anlagen will be acconnplished in connection with limb operations.) 



OBSERVATIONS AND EXPERIMENTAL DATA: 



Under each sub-heading for Extirpations, follow the development of each embryo with a 

 series of sketches. The first drawing should be made immediately after the excision, 

 and the last one after the excised area has been completely reformed, whether or not it 

 is regenerated. The time elapsed (days) and, the medium and temperature should all be 

 noted. (See section on "Wound Healing". ) 



REFERENCES 



ADELMANN, H. B. , 1937 - "The effect of the partial and complete excision of the prechordal substrate on the development of 



the eyes of Amblystoma punctatum." Jour. Exp. Zool. 75:199. 

 BODENSTEIN, D. , 1943 - '*An analysis of balancer development in Triturus torosus. " Physiol. Zool. 16:44. 

 COPENHAVER, W. M. , 1939 - "Initiation of the beat and intrinsic contraction rates in the different parts of the Amblystoma 



heart." Jour. Exp. Zool. 80:193. 

 DETWILER, S. R. , 1946 - "A quantitative study of locomotion in larval Amblystoma following either midbrain or forebrain ex- 

 cision." Jour. Exp. Zool. 102:321. 

 EKMAN, G., 1929 - "Experimentelle Untersuchungen uber die fmheste. Herzentwicklung bei Rana fusca. " Arch. f. Ent. Mech. 



116:327. 

 HARRISON, R. G. , 1924 - "The development of the balancer in Amblystoma, studied by the method of transplantation and its 



relation to the connective tissue problem. " Jour. Exp. Zool. 41:349. 

 KOLLROS, J. J., 1940 - "The disappearance of the balancer in Amblystoma larvae." Jour. Exp. Zool. 85:33. 

 PETERSEN, H. , 1923 - "Berichte uber Entwicklungsmeckanik. I." Ergebn. d. Anot. u. Entw'gesch. 24:327. 

 ROTMANN, E. , 1935 - "Der Anteil von Induktor und reagierendem Geweb an der Entwicklung der Kiemen und ihrer Gefasse. " 



Arch. f. Ent. Mech. 133:225. 

 SCHOTTE, O. E. , G M. V. EDDS, 1940 - "Xenoplastic induction of Rana pipiens adhesive discs on balancer site of Amblystoma 



punctatum." Jour. Exp. Zool. 84:199. 

 SEVERINGHAUS, A. E. , 1930 - "Gill development in Amblystoma punctatum. " Jour. Exp. Zool. 56:1. 

 STOHR, P., 1929 - "Zur embryonalen HerTtmnsplantation." Arch. f. Ent. Mech. 109:300. 



"There is fundamentally a natural corrective for our inclination to 

 allow likes and dislikes to influence our reason. This corrective is found 

 in the instinct of curiosity, the faculty that impels men to seek the truth, 



even if it be unpalatable . " 



A. J. Lotka 



