THE PHENOMENA OF MUTATION 195 



portion of rabbit's thyroid, to the other a piece of 

 rabbit's liver. They fed eagerly on both. After- 

 wards I obtained at intervals of a week or so the 

 thyroid of a sheep. I have seen no precise details of 

 Gudernatsch's method of feeding tadpoles, but my 

 own method was simply to put a piece of thyroid 

 into the water containing the tadpoles and leave it 

 there for several days, then to take it out and put in 

 another piece, changing the water when it seemed to 

 be getting foul. 



April 22. Noticed that the non-thyroid tadpoles 

 were larger than those fed on thyroid. Changed the 

 former into the pie-dish and the latter into the glass 

 jar, to make sure that the difference in size was not 

 due to larger space. 



May 3. Only eighteen of the non-thyroid tadpoles 

 surviving, owing to the water having become foul, 

 but these are three times as large as those fed on 

 thyroid. In the latter no trace of hind-legs was 

 visible, but the abdominal region was much emaciated 

 and contracted, while the head region was broader. 



May 4. Noticed minute white buds of hind-legs in 

 the thyroid-fed tadpoles. 



May 6. A number of the thyroid-fed were dying, 

 and the skin and opercular membranes were swollen 

 out away from the tissues beneath. 



Largest normal tadpole, . . 2*7 cm. long. 



body, 1-0 



tail, 1-7 



Largest thyroid-fed tadpole, 1*1 cm. long. 



body, 0-5 

 tail, 0-6 



May 10. A great number of the thyroid-fed dead 



