212 CAREY P. McCOED AND FLOYD P. ALLEN 



larvae the parietal organ again assumes control. Laurens has 

 completely disproven this hypothesis (11). 



It is noteworthy from the present study that although the 

 pineal gland does not exert a controlling influence upon pig- 

 mentation comparable to that arising from environmental stim- 

 ulation of the retina, nevertheless it contains an active substance 

 capable of directly inducing pigmentation changes irrespective 

 of environmental conditions. 



MATERIAL AND METHODS 



Eggs of the species Rana pipiens, Rana cantabrigiensis and 

 Bufo Americana were collected in the vicinity of Detroit, and 

 hatched in the laboratory. Immediately after hatching and 

 before the oral orifice had opened they were grouped in trays 

 into colonies of 200 and food placed in the trays. The food was 

 weighed, each colony receiving the same amount triweekly. 

 All foods were taken voraciously by the tadpoles. By means 

 of a water dropping and disposal system the tadpoles were at 

 all times in fresh, aerated tap water. Moreover the trays were 

 frequently shifted to average environmental conditions of light 

 and temperature. In the observations on pigmentation we 

 used some 12,000 tadpoles. 



The food consisted of desiccated glandular material and fresh 

 plant food. Of the glands we tested the effect of pineal (adult 

 and preadult) thyroid, parathyroid, and suprarenal. Brain 

 tissue and beef muscle were used as controls. Different lots 

 of tadpoles were fed upon Spirogyra, bread crumbs and hemp 

 seed as a further check. A single lot of tadpoles was fed on 

 desiccated retinae from beef eyes as a particular experiment. Of 

 these tissues the pineal gland alone produced the phenomenon 

 we have called the pineal-pigment cycle. 



EXPERIMENTAL EVIDENCE 



Effect of whole pineal tissue on pigmentation 



Certain endocrinous tissues are known to alter pigmentation 

 in tadpoles. This was noted by Gudernatsch (12), in his feed- 



