THE THYROTROPIC HORMONE 



vented by the removal of the anterior lobe or the buccal 

 anlage of the pituitary, because what is now termed thyro- 

 tropic hormone is no longer available. Without thyrotropic 

 hormone from the anterior pituitary, thyroid function is so 

 deficient that metamorphosis is prevented. The experiments 

 of Voitkevic (1937), who used larvae of Rana esculenta and 

 R. temporaria^ confirm observations — i.e., such as the greater 

 thyrotropic efi?"ect of implants of basophilic chromophils in 

 comparison with oxyphilic chromophils — which have already 

 been discussed in my monograph of 1936. The author's ob- 

 servation that implants of beef anterior pituitary containing 

 oxyphils as the principal chromophil antagonize spontaneous 

 metamorphosis or metamorphosis caused by anterior pituitary 

 basophils or thyroid extract has not been independently con- 

 firmed. Etkin's study (1935), in which larvae of /?. sylvatica 

 were used, led to the following conclusions: (i) The pars 

 buccalis is self-differentiating (i.e., differentiation occurs after 

 its transplantation to a new site), (2) thyrotropic hormone is 

 secreted in an amount proportional to the amount of actively 

 secreting pituitary tissue, and (3) the liberation of the hor- 

 mone appears not to depend on nerves. Metamorphosis oc- 

 curred at about the normal age and stage of growth in em- 

 bryos which had been hypophysectomized and given re- 

 placement therapy in the form of a transplant of the re- 

 moved pituitary which was placed in the eyecup or under 

 the adhesive disk. If similar embryos received three trans- 

 plants of the pars buccalis under the adhesive disks after 

 hypophysectomy, precocious metamorphosis (at 8 instead of 

 the normal 18 days) followed; also, the length of the larvae 

 was less than that of normal larvae at the time of the cor- 

 responding change (29 instead of 44 mm.). According to 

 Atwell (1935), the differentiation and subsequent secretory 

 activity of the anterior pituitary in larvae of R. sylvatica or 

 R. pipiens can take place without contact with nervous tissue 

 or foregut. (Atwell could not be sure that this statement 

 holds for the pars intermedia; also, he stated that Etkin's 



[175] 



