Jan., 1913.] Pigment Development in Spelerpes Larvae. 53 



Experiments with Resorcinol. 



A total of 150 experiments, including 103 which had as their 

 aim the test of the effect of varying length of immersion in the 

 drug, were conducted using 636 larvae, not including checks in 

 each series. We find that resorcinol is more potent than orcinol, 

 not alone in being more toxic, but the type produced by it is, if 

 possible, more definite. The same swellings of the serous cavities 

 are produced if the eggs are treated before reaching the late neural 

 groove. When treated before reaching the blastula, no larvae 

 were hatched. 



When larvae which had the head strongly differentiated or 

 were in any stage between this and a day or two after the begin- 

 ning of pigmentation, were treated with resorcinol in sufficient 

 concentration (0.020% to 0.025% and in one instance 0.05%) 

 and for a sufficient length of time (4 to 10 or more days) they were 

 highly modified and produced one of two types. Both types 

 begin with a retardation of development and a great retardation 

 of pigmentation. The first pigment appears in the eye and in a 

 day or two a narrow V appears on the shoulders, followed 

 a little later by a narrow line down the spine. This condition 

 persists as long as the larvce remain in the resorcinol, but unfor- 

 tunately the drug is so toxic that 15 to IS days immersion invari- 

 ably causes death. We have had many instances where the larvae 

 which were treated with resorcinol appeared almost entirely 

 devoid of pigment except for the dark eyes, when the correspond- 

 ing checks were completely piginented and the spots were fully 

 developed. 



When the larvae are removed from the resorcinol solution after 

 varying lengths of time we obtain the same two types referred to 

 above. The more extreme type (See Fig. No. 1) resembles the 

 "orcinol type" but is heavier, the "flippers" are more enlarged, 

 and the pigment reticulation is very fine as contrasted with the 

 coarse reticulations of the orcin type. This type persists for 60 to 

 70 days when death by starvation ensues. 



The second type probably represents those individuals which 

 have not been so profoundly modified. The body fomi is almost 

 normal, the limbs and toes are well developed, but the spots are 

 absent and the pigment pattern is very fine and dull in color. 

 The majority of this type also die of starvation, and on Dec. 6 — 

 about 161 days from the beginning — we have only a very few 

 individuals remaining. None of these have been "typical" but 

 have been classed as "fair resorcin" or "somewhat modified" 

 and all but two of these larvae still show modification. At this 

 period of development, however, the checks have lost their charac- 

 teristic markings so that a closer analysis is impossible. In 

 nearly every instance in both the orcinol and resorcinol series, the 

 surviving individuals are lighter than the checks. 



