PIGMENT CHANGES IN ANURAN LARVAE 123 



The pars intermedia is a transverse band of tissue with bulging 

 lateral terminations, closely applied to the anterior lobe. Pos- 

 teriorly it conforms so closely to the shape of the pars nervosa that 

 it is difficult to make a clean-cut dissection of the two parts under 

 the microscope. The texture and color of the tissue of the two 

 two lobes differ to such an extent, however, that is is easy to 

 distinguish them. 



OBSERVATIONS 



Forty-seven larvae, light greenish-yellow in color, were engrafted 

 intraperitoneally with the pars intermedia of the hypophysis of 

 the three species of Rana mentioned. Sixteen hours after the 

 operation, the experimented animals were distinctly darker than 

 the controls, and at the end of forty-eight hours they were nearly 

 black. The controls, engrafted with brain and muscle tissue, 

 retained the normal light-greenish yellow color (fig. 2). The 

 change in color following the operation is very striking, indeed, 

 on account of the color contrast between control and hypophy- 

 sis-grafted tadpoles, and also because it is so uniform. Any 

 possibility of the environment's playing an active role in the 

 reaction was ruled out by the controls, although it is quite true 

 that chloretone tends to cause slight expansion of the melano- 

 phores. It was observed that after anaesthetizing the control 

 tadpoles in chloretone the animals turned somewhat darker ten 

 to twenty minutes afterward; this condition lasted but a short 

 time, after which the larvae resumed their normal coloration. 

 The reaction was not at all comparable to the striking effects 

 following transplantation of the pars intermedia (fig. 2). 



The darkly pigmented condition persists in the engrafted ani- 

 mals for varying periods, but in none did it last longer than forty 

 days. It has been my experience that the larvae engrafted with 

 the glandular tissue from adult frogs of different species, i.e., het- 

 eroplastically grafted, are the first to return to normal coloration. 

 Animals homoplastically grafted tend to retain the dark color for 

 longer periods, though this is certainly not an invariable rule. In 

 the case of heteroplastic transplants, twenty-six days was the 

 maximum and ten days the usual period for the retention of the 



