PIGMENT CHANGES IN ANURAN LARVAE 125 



been resorbed; that is, the glandular tissue has disappeared, and 

 nothing remains of the transplant but a mass of connective tis- 

 sue and blood vessels. On the other hand, in the black individ- 

 uals the engrafted tissue always shows the presence of secreting 

 glandular cells. The transplanted tissue of the hypophysis in 

 both hetero- and homoplastic grafts evidently is largely resorbed 

 in bullfrog larvae of 55 mm. total length about twenty-six days 

 or less from the date of transplantation. The transplanted tissue 

 is generally found attached to the peritoneum of the body wall 

 and is much more satisfactorily handled for microscopic examina- 

 tion when left attached to a section of the somatopleure than when 

 separated from it. Otherwise, the minute size of the graft renders 

 handling difficult. The implanted pars intermedia very soon 

 becomes invaded with blood vessels from the peritoneum. Allen 

 ('20) failed to state whether or not any of his animals resumed 

 normal coloration following transplantation of the pars inter- 

 media, nor was any histological examination made to ascertain 

 the fate of the graft. A more detailed report by Professor Allen 

 upon this point is awaited with interest. 



Several tadpoles, previously darkly pigmented by reason of the 

 engrafted tissue of pars intermedia, but which subsequently re- 

 sumed the yellow color owing to resorption of the transplant, were 

 reengrafted. The results were always the same, the animals 

 turned very dark for several weeks, then returned gradually to 

 normal coloration. Aside from the more rapid resorption of the 

 grafted tissue of other species of frogs, it apparently made 

 no difference in my experiments, so far as the results were 

 concerned, whether the transplant was homo- or heteroplastic in 

 nature. This is more or less to be expected in grafts involving 

 endocrine glands, owing to the presence of the physiologically 

 active hormone in the glandular substance transplanted. Even 

 though the graft be resorbed, a sufficient amount of the active 

 hormone is generally obtained to bring about a response on the 

 part of the organism. ^ , In a recent series of experiments with 



1 The pigmentary changes are more marked when the pars intermedia and 

 pars nervosa are transplanted together, than when the intermediate lobe is 

 grafted alone. The inclusion of the posterior lobe causes a remarkable shrink- 

 age of the larvae due to the diuretic effect upon the mesonephros and conse- 

 quent loss of turgor by rapid elimination of water. 



