338 



C. C. SPEIDEL. 



TABLE I. 



In this table is given for each species of tadpole the number of individuals 

 observed with prior left forelimb eruption as compared with the number of indi- 

 viduals observed with prior right forelimb eruption, under normal conditions, 

 under thyroid treatment and under thymus treatment. 3 



Under normal conditions a definite majority of tadpoles puts 

 out the left forelimb first; in Hyla 72 per cent., in Rana syhatica 

 65 per cent. The few observations upon untreated bullfrog and 

 green frog tadpoles in the three-limb condition support Dicker- 

 son's observation that the left limb usually erupts first. Under 

 thyroid treatment the left forelimb is invariably protruded first 

 in all species studied, if those putting out forelimbs during the 

 first forty hours of the treatment are excluded. Under thymus 

 treatment apparently a i : I ratio is indicated. The experiments 

 with Hyla afford the best comparative figures and may be taken 

 as typical. 



With thyroid treatment of half-grown tadpoles 100 per cent, 

 put out the left forelimb first. A special experiment was tried 

 in which 75 Rana syhatica tadpoles were subjected to thyroid 

 treatment, many of these at the time being on the verge of putting 

 out the forelimbs. Among those animals putting out forelimbs 

 within the first forty hours, seven righthanded ones were seen; 

 thereafter all were lefthanded. It may be concluded that in 

 animals protruding the forelimbs within (his time, an original 

 bias toward righthandedness may not be changed. In a similar 

 experiment with 25 Hyla tadpoles that were also fairly close to 



1 For reasons explained in the text all animals putting out forelimbs within the 

 first two days of thyroid or thymus treatment are discarded, and do not figure 

 in the table. 



