3 20 



HOMER W. SMITH AND G. II. A. CLOWES. 



water, as is the case in Arbacia and Astcrias, and comparatively 

 close to the limits of acid tolerance. 



The scarcity of material made it impossible to examine more 

 closely the influence of reaction on the physical properties of the 

 Chcetopterus egg. It may be stated, however, that unlike Astcrias 

 and Arbacia, the Chcetoptcrus egg is distinctly liquified rather than 

 solidified at pH 4.6 to 5.0. This liquefaction is so marked that 

 after an exposure of one or two hours the eggs are extremely fluid 

 and will flow into thin pencils when the containing vessel is tilted or 

 jarred. A similar liquefaction takes place from pH 9.0 to 10.0. 



There is no doubt that physical changes in the nature of coagu- 

 lation in acid and dispersion in alkali characterize the limits of 

 physiological tolerance in Arbacia and Astcrias eggs. But that 

 coagulation in acid is not the invariable rule is evident from the 

 liquefaction which occurs in Chcetopterus eggs. It is reasonable 

 to suppose that the specific composition of the cortex (and per- 

 haps of the vitelline membrane as well) determines both the di- 

 rection and degree of the physical changes at various reactions. 

 The cytoplasm of all the eggs examined here is distinctly liquid 

 (13) and it may be that the liquefaction or gelation observed is 

 more a consequence of changes in the vitelline membrane and 

 cortex than in the cytoplasm proper. 



The general nature of the changes in physical properties and 

 the changes accompanying ageing at various H-ion concentrations 

 suggests that the prolongation of the life of these eggs in acid 

 solution is a consequence of reduced metabolism. Increasing 

 acidity up to a certain point leads, perhaps by an internal action 

 or by a reversible alteration in the cortex which decreases the 

 facility of interchange, to decreased metabolic activity; excessive 

 acidity on the other hand produces irreversible injuries in the egg; 

 where reduced metabolism and acid injury strike a reversible 

 mean, the egg retains its viability for the longest time. The agree- 

 ment between the pH at which maturation of Asterias eggs is 

 completely inhibited and the pH of maximum viability conforms 

 with this suggestion. The H-ion concentration of maximum 

 viability may have some significance in relation to ovarian life, 

 for in the ovary the egg is subjected to a greater CO 2 tension and 

 H-ion concentration than that of sea water. But the coelomic 



