464 MINNA E. JEWELL 



Finally, Grace Medes ('18) has shown that changes in the 

 composition of the sea-water by concentration, dilution, or 

 addition of acids, bases, or salts in non-lethal concentrations 

 cause a retardation of development of the eggs of Arcabia 

 punctulata. 



Excepting for the experiments of Loeb in 1898 on Fundulus 

 eggs, nearly all of the work so far done on the effects of bases 

 and acids on development has been done upon marine animals. 

 Many of the most serious difficulties in such investigations arise 

 as the result of the chemical composition of sea-water, and may 

 be largely eliminated by the use of fresh-water forms. Thus 

 Haas ('16) has shown that the addition of hydroxides to sea- 

 water results in a proportionate increase in OH ion concentration 

 only after all of the Ca and Mg have been precipitated out in 

 the form of their basic carbonates. This discovery is of twofold 

 importance, for it means, in the first place, that much of the base 

 added to the sea-water is immediately thrown out, and, in the 

 second place, a disturbance of the balance between the salts of 

 Na, K, Ca, and Mg, which Loeb ('03) has shown is exceedingly 

 harmful to marine animals. 



In working with acids, too, the use of sea-water presents 

 certain difficulties, for any strong acid added to sea-water will 

 immediately form salts with the liberation of CO2. Hence no 

 comparison of the effects of the various mineral acids is possible, 

 as the acidity existing in the sea-water is due to H2CO3. For 

 this reason, and also to see whether fresh-water animals are 

 adjusted to a different H ion optimum than marine organisms, 

 the author at first wished to undertake a study of the effects 

 of bases and acids upon development and growth in some fresh- 

 water form. Since, however, there were no eggs or young 

 larvae available at the time of year when this investigation was 

 commenced, it was decided to use regeneration which in many 

 ways resembles original growth. This seemed further desirable 

 because no such studies of regeneration have as yet been made, 

 and it is probable that comparative studies of regeneration 

 and growth under varying environmental conditions may throw 

 much light upon the extent of the similarity or dissimilarity of 



