Jan., 1913.] Pigment Development in Spelerpes Larvae. 51 



with dense black pigment; and (3), the dense dull-black color of 

 the larvae compared with which the check often appears very light. 



There is no mistaking the ''tyrosin type", for an inexperienced 

 person will always pick them out as the darkest individuals 

 in a series. 



Of the 21 experiments which showed an effect, 15 had a tyrosin 

 concentration of 0.010%, 1 of 0.012.3%, 2 of 0.020%, 1 of 0.040%, 

 and 1 of 0.006% (this last being the only one of the entire 41 

 experiments which showed an effect at this concentration, and 

 which, as noted above, "reverted" after the 2Sth day). 



The time of treatment averages about 60 days, and in three 

 experiments (Nos. 560, 595, 609) which are still running (Dec. 6) 

 the larvfe were in tyrosin for 72 days and have since been in pure 

 water only (no tyrosin) for 123 days. They are still appreciably 

 darker than the corresponding checks, and show enough of the 

 characteristics of the "tyrosin type" to be readily classified as 

 such. During the later period the larvae have at least doubled 

 their previous length, but it is impossible to say whether their 

 continued darker color is due to a continued more active pigment 

 formation or merely to a distribution over a larger area of the 

 dense black mass of pigment already present! . 



Experiments with OreinoJ. 



Orcinol, as noted above, inhibits the action of tyrosinase upon 

 tyrosin in the test tube, and we hoped to be able to inhibit, or at 

 least to modify, the course of pigment development by rearing the 

 larvcC in solutions of orcinol. We found the drug to be quite 

 toxic, not so much so of itself as the oxidation products which are 

 formed by the action of light upon a solution of orcinol. However, 

 by changing the solutions every day, or every second day, and 

 keeping the dishes, together with the controls, in a dimly lighted 

 room, we were able, in part, to prevent the toxic action. In this 

 manner we have been able to keep larvaj in a solution of 0.020% 

 concentration for 50 days. 



Altogether 35 experiments were run, including 513 individuals 

 (not including checks). Later it seemed advisable to subdivide 

 some of the experiments so as to accurately test the effect of 

 varying length of immersion in the drug solution. A total of 115 

 such removals were made, each one in reality being a separate 

 experiment in itself, thus making a grand total of 150 experimelits. 

 Concentrations of orcinol ranging from 0.0125% to 0.025%:^w^re 

 employed. \f 



t As the larvae become older the characteristic spots of the checks 

 become less conspicuous and are later lost so that the types become less 

 differentiated, and the depth of color is about the only criterion available 

 at this stage of development. 



^.^^ 



