INFLUENCE OF HYDROGEN ION CONCENTRATION. 325 



ing the eggs in sea water to which various substances had been 

 added. She found that HC1, CO 2 and acetic acid markedly re- 

 tarded development. In view of Loeb's statement that alkali does 

 not have any effect on the early development of Arbacia, she re- 

 examined this point by counting the number of divided eggs one 

 hour after insemination, and by comparing the skeletal develop- 

 ment of the larvae 18 hours after insemination. She found a 

 definite acceleration from one to 18 hours with NaOH (greatest 

 in 1.33 cc. N/io NaOH -f- 98.66 cc. sea water) and with Na 2 CO 3 

 (greatest in 0.4 cc. 0.45 M. Na 2 CO 3 + 99.6 cc. sea water), though 

 in later stages the alkali cultures showed a retardation so that ulti- 

 mately they lagged behind the controls. Larger quantities of 

 NaOH and Na 2 CO 3 inhibited development from the beginning. 

 NaCl produced slender, perforated skeletons with conspicuous 

 processes; there was inhibition during early development and ex- 

 cessive growth during later periods. NaOH led to irregularity 

 and asymmetry, while NaHCO 3 increased the bulk of the skeleton 

 with a strong tendency for regularity and symmetry. 



Richards (9) has recently observed acceleration of the early 

 cleavage rate of the eggs of the opisthobranch, Haminca vircscens. 

 in sea water to which NaOH and KOH had been added. No 

 acceleration was observed after the addition of Ba(OH), and 

 Cr(OH) : , 



In none of the investigations cited were the H-ion concentra- 

 tions determined or controlled, nor was allowance made for any 

 specific influence which the carbonic acid present in acidified sea 

 water might have. Knowing that carbonic acid inhibits cell di- 

 vision at H-ion concentrations which otherwise are innocuous 

 (10), it is important to determine the limits of reaction of CO 2 - 

 free sea water within which normal development is possible. 



In performing the experiments reported in this paper, Arbacia 

 and Astcrias eggs were inseminated in sea water and subsequently 

 transferred to icocc. of the pH solutions prepared as described 

 in a previous paper ( 1 1 ) . At appropriate intervals samples of 3 

 to 5 cc. were removed from each lot and fixed by the addition, in 

 the case of Arbacia, of 2 or 3 cc. of a i-iooo solution of formalin 

 in sea water ; the Astcrias eggs were fixed by adding 2 or 3 cc. of 

 a i-iooo mercurv bichloride solution in sea water. These meth- 



