150 LESLIE B. AREY 



question coiict>rniii^' tlio correspoiulenco of their body temperature 

 and that of the surrounding^ medium. 



What would be discovered in a study of earher stages I can 

 not say, but I suspect great difhculty would be encountered in 

 interpreting the results due to incomplete pigmentation, for 

 the differences at various temperatures in the 4.5 cm. tadpole, 

 although fairly well marked, showed much less contrast than those 

 exhibited by the 7.0 cm. animals. 



3. Necturus. A comparison between the frog and some uro- 

 dele suggested another interesting problem. Is the condition 

 exhibited in the frog restricted to anurans or is it common to 

 the whole group of amphibians? This query becomes all the 

 more pertinent when it is recalled that urodeles are not in the 

 direct line of ascent to the anurans; that is, they are not amphib- 

 ians which have never gone beyond the water inhabiting stage, 

 but are more probably a group that were once land animals 

 and have again returned to the water as a secondary adaption. 



The common mud puppy, Necturus maculatus, was chosen 

 because of the ease with which it is procured and kept in cap- 

 tivity. These animals were treated according to the technique 

 used for fishes, hence a temperature higher than 28°C\ was 

 not attempted. 



The first experiments performed were to secure typical light- 

 and dark-adapted retinas in order that some basis of compari- 

 son might be had. The results were by no means as striking as 

 one might wish. In both cases the pigment was extended, not 

 in a band with even contours, but generally in large conical proc- 

 esses from the individual cells, which, hke other cells of Necturus, 

 appear to be very large; these conical processes surround the 

 distal ends of the outer segments of the rods. 



In the Hght, the pigment was usually somewhat more ex- 

 tended than in darkness. The processes were not of uniform 

 length but mean measurements may be expressed by the values 

 of about 38 n in the light and 30 /x in the dark, — ^a condition 

 of slight contrast when compared with fishes or the frog. The 

 presence of a certain amount of migration in Necturus has 

 been previously noted by Howard ('08), who took advantage of 



