310 HOMER W. SMITH AND G. H. A. CLOWES. 



eggs and blastuke, irregular cleavage as manifested in change of 

 size and shape of the blastomeres, retardation in the rate of cleav- 

 age, and in extreme stages a total loss of the capacity to cleave. 

 There is also an increase in volume and a loss of the jelly normally 

 surrounding the fresh egg ; in To.vopneustes and Hipponoe there 

 is an initial acceleration in the rate of membrane formation, and 

 in all three species a subsequent retardation of this rate and ulti- 

 mately a complete loss of the capacity to lift a membrane. Gold- 

 farb attributed the changes accompanying ageing principally to 

 changes in the cortical layer, which, he states, are in turn refer- 

 able to changed metabolism. 



Our results confirm Goldfarb's findings in respect to the loss in 

 Arbacia of the capacity to divide. This is equally true at all H- 

 ion concentrations. In Asterias, however, on the alkaline side of 

 the optimum the capacity to divide is lost before the capacity for 

 membrane formation. But on the acid side of the optimum (pH 

 6.2 to 6.5) practically all eggs which lift membranes develop 

 through the first few cleavages. 



In both species the tendency for polyspermy increases in pro- 

 portion to the physiological, rather than the temporal, age of the 

 eggs. Consequently, the incidence of polyspermy is decreased at 

 the optimum to about the same extent to which the viability of 

 the eggs is increased. It is difficult to distinguish polyspermic 

 from abnormally dividing eggs without cytological examination, 

 and therefore it is deemed inadvisable to draw conclusions from 

 our data concerning the tendency for polyspermy after ageing at 

 various H-ion concentrations. It may be said, however, that 

 among those eggs which are aged from pH 6.2 to 6.5 there is a 

 decidedly lower incidence of both definite polyspermy and irregu- 

 lar division, as contrasted with eggs which are aged in more alkaline 

 solutions. The former, if they divide at all, tend to divide regu- 

 larly through at least two or three cleavages. 



The ageing of Arbacia and Astcrias eggs in sea water is accom- 

 panied by a slight increase in volume and fluidity. The nucleus 

 which is difficultly discernible in the fresh mature egg, appears 

 in the stale egg as a distinctly defined, hyaline vesicle near the 

 center of the egg. Later, when the egg loses its fertilizing capac- 

 ity, the cytoplasm becomes distinctly granular and opaque and 



