462 MINNA E. JEWELL 



Probably no single environmental factor is of greater impor- 

 tance to aquatic animals than the chemical reaction (hydrogen 

 ion concentration) of the water. Shelf ord and Powers ('15) 

 have shown that marine fishes are extremely sensitive to slight 

 variations in the hydrogen ion concentration of the water, and 

 Wells ('15) has shown the same to be true of fresh-water fishes. 



The first study of the effect of hydrogen ion concentration 

 upon the rate of development is that of Loeb ('98) . He compared 

 the development of eggs of the sea-urchin in normal sea-water 

 with those in sea-water to which 2 cc. O.IN NaOH per 100 cc. 

 had been added. At first no difference was noted, but after the 

 thirty-two- to sixty-four-cell stages it was evident that the eggs 

 in the alkaline solution had developed more rapidly. The 

 embryos in normal water were still blastulae when those in 

 alkaline water were plutei, and at the end of forty-eight hours, 

 though all were plutei, the ones in alkaline water were larger, 

 and further developed. One, two, or three cc. O.IN HCl per 100 

 cc. was found to retard development. 



Working upon the eggs of Fundulus in fresh water, Loeb 

 found that 4 cc. O.IN NaOH per 100 cc. caused them to hatch 

 faster. More than 6 cc. retarded development; 12 cc. allowed 

 only a few of the eggs to hatch, while 15 cc. resulted in failure 

 of any to hatch. Two cc. of O.IN HCl killed all of the eggs, 

 while 1 cc. killed most of them. Loeb attributes these results 

 to an increase of oxidation by bases and a decrease by acids. 



Later Loeb ('14) decided that the acceleration of development 

 of the sea-urchin eggs in water to which NaOH had been added 

 did not appear until the thirty-two- to sixty-four-cell stage 

 because at first the concentration was too high, but after a few 

 hours the beneficial effects appeared as the result of neutralizing 

 the acids produced by the embryos during development. These 

 conclusions were based upon a comparison of the rate of regener- 

 ation and growth of tubularians in a solution of NaCl, KCl, 

 CaCl2 and MgClo in the proportions in which they occur in sea- 

 water, and in the same solution to which NaOH, NaHCOs, or 

 Na2HP04 had been added. Although the growth was invari- 

 ably better when a base had been added, as the effects of the 



