THE PARS BUCCALIS OF THE HYPOPHYSIS 33 



although of an identical nature, is more slowly evoked. In 

 determining the possible cause for this tardy response, the work 

 of Levy is particularly suggestive. This investigator has shown 

 that the reponses to adrenahn are more rapid if the thyroid 

 has been stimulated or its extract injected. Although it has 

 not been shown to what extent these responses of the pigment 

 cells are referable either to the adrenal or directly to the sym- 

 pathetic nervous system, still the slower responses of thyroidless 

 larvae may well be of considerable significance in view of Levy's 

 work. Fm-thermore, since pigment cells are formed and react 

 in the thjToidless specimens in an identical manner with those 

 of the normal, it is apparent that neither their atjrpical forma- 

 tion nor reaction in the albino can be referred to the atrophy 

 of the thyroid effected by the hypophysectomy. 



It has been shown that the epidermal melanophores of the 

 • posterior-lobe-fed hypophysectomized specimens exhibit a uni- 

 form state of great contraction, a contraction that persists for 

 an extended period after the substitution of some other diet. 

 WiU these cells then respond to light and heat as do those of 

 the typical albino? 



It will be recalled that in the typical albino these cells, unlike 

 the xantholeucophores, are sensitive to brilliant illumination 

 coincident with increased temperature, undergoing an expansion. 

 But the epidermal melanophores of the posterior-lobe-fed albinos 

 stubbornly maintain their contracted condition with this stimu- 

 lus and appear incapable of responding. Lest it be supposed 

 that the reaction of these cells has approached that frequently 

 exhibited by normal larvae, one need only to try their response 

 to complete darkness where normal behavior would give us full 

 expansion. Under all circumstances, their contracted condition 

 is maintained just as is the corresponding persistent expansion 

 of the xantholeucophores in these hjrpophysectomized larvae. 



It was highly interesting to note that an abrupt change in 

 the diet of the posterior-lobe-fed albinos, a substitution of a 

 liver diet, led gradually to a resumption of the response char- 

 acteristic of the typical albino. After an interval of one week 

 in which they have received no nervous hypophysis they become 



MEMOIR NO. 11. 



