Septembeb 2, 1910] 



SCIENCE 



317 



us from Garret County, Maryland. In north- 

 ern New Jersey, where both species of toad 

 occur, the American toad is conspicuous only 

 during the breeding season. In midsummer 

 almost all the toads that are found hopping 

 along the roadside at dusk are Fowler's toads. 

 This apparent scarcity of the northern toad 

 may be due to its habits; it may stay more in 

 the woods, or come out later at night. 



At Newton, N. J., in mid-June, a number 

 of fine specimens of americanus were found 

 in the long grass of a moist meadow border- 

 ing a cat-tail marsh, associated with pickerel 

 and leopard frogs. No individuals of fowleri 

 were found in the meadow, all, with one ex- 

 ception, being seen along the roads in the 

 evening, where also a few examples of ameri- 

 canus were taken. 



The diiference in the time of breeding of 

 the toads is well known. On Staten Island 

 the song of Fowler's toad is first heard about 

 April 20, when the American toads at Van 

 Cortlandt Park, N. Y., have already begun to 

 leave the water. 



Bufo americanus and 5. fowleri are certainly 

 to be looked upon as distinct species rather 

 than as geographical races, yet we have taken 

 a number of toads on the Palisades, and on 

 the northern end of Manhattan Island, which 

 we can not refer satisfactorily to either. 

 Most of them are intermediate in regard to 

 the size of the warts, and a few are as smooth 

 as Fowler's toads but with black spots on the 

 breast. They may represent only the extremes 

 of variation, or they may perhaps be hybrids. 

 This is a question which could be settled 

 only by experimental study, but that there is 

 some possibility of hybridization is shown by 

 the following incident: A male American 

 toad, during the spring of 1909, which was 

 put in a cage with some frogs, was later found 

 clasping a female pickerel frog (Bana palus- 

 tris) to which he clung for several days. 

 Would not such an individual, if unsuccess- 

 ful in securing a mate of his own species, be 

 quite likely, a little later, to fertilize the eggs 

 of a female Fowler's toad? 



W. DeW. Miller, 

 James Chapin 



FURTHER PROOFS OF THE INCREASE IN PERME- 

 ABILITY OF THE SEA URCHIN's EGG TO ELECTRO- 

 LYTES AT THE BEGINNING OF DEVELOPMENT 



Using Kohlrausch's method, I observed an 

 increase in electric conductivity of the sea 

 urchin's egg at the beginning of development, 

 indicating an increase in permeability to ions. 

 Although only one proof is necessary to estab- 

 lish a fact, it is interesting to see other data 

 fall into line. 



If an electric current is passed through the 

 egg of Arhacia punctulata, the cytoplasm be- 

 gins first to disintegrate in the region nearest 

 the anode. The red pigment diffuses out of 

 the plastids in this region and turns an orange 

 hue.* This is most probably due to the ac- 

 cumulation of anions, which dissociate water, 

 forming acids, and indicates a poor perme- 

 ability of the plasma membrane to anions. 

 As no corresponding disintegration takes place 

 at the cathode end, the plasma membrane must 

 be more permeable to cations than to anions. 



If fertilized and unfertilized eggs in sugar 

 solution be placed on the same slide under the 

 microscope and an electric current of gradu- 

 ally increasing strength passed through, the 

 unfertilized eggs begin to disintegrate sooner 

 than do the fertilized eggs. This difference is 

 also true after the fertilization membrane has 

 been shaken off. Therefore, the unfertilized 

 eggs are less permeable to anions than are the 

 fertilized eggs.' A low permeability to anions 

 means a low permeability to electrolytes, since 

 the cations on leaving the egg would be 

 pulled back by the negative field produced by 

 the excess of anions confined, and only the un- 

 dissociated molecules could diffuse freely. 



Since it has been shown that unfertilized 

 eggs are less permeable to anions than are 

 fertilized eggs, we should expect it to be more 

 difficult to plasmolyze unfertilized than fer- 

 tilized eggs with solutions of non-electrolytes. 

 In solutions of non-electrolytes, the electro- 



" A solution of the pigment turns pale orange 

 in acid and deep purple and is precipitated in 

 alKali. 



■ Or the electrolytes have diffused out of the 

 fertilized more than from the unfertilized eggs, 

 in either case showing increased permeability. 



