202 CARNEGIE INSTITUTION OF WASHINGTON. 



lowered percentage of eggs that cleaved, and a change in then- development. 

 These results suggested that other factors connected with over-ripening of 

 germ-cells be studied with a view towards obtaining a more adequate chemico- 

 physical explanation of the phenomena associated with the aging and death 

 of germ-cells. As the inquiry extended, it was found increasingly desirable to 

 concentrate upon the changes in the egg alone, and to postpone for a later 

 opportunity the more detailed study of the sperm-cell. The sea-urchin Hip- 

 ponoe was used for this summer's work at Tortugas, Florida. 



The investigation extended principally along five lines, namely: (1) 

 changes in the jelly envelope; (2) changes in volume of the egg; (3) effects 

 of temperature; (4) changes in the cortical layer; (5) respiration of aging eggs. 



Changes i.v the Jelly Envelope. 

 Eggs freshly shed or removed from the body were nearly always sur- 

 rounded by a thick hyaline envelope, which was made strikingly clear by 

 Chinese-ink solution. At successive intervals the eggs kept in bowls of sea- 

 water just below room temperature lost the jelly envelope more and more 

 completely, and the extent and rate of disappearance was ascertained. It 

 was found that in the beginning there was little or no disappearance of the 

 jelly, followed by a period of rapid dissolution, and finally, all, or very nearly 

 all, the eggs were without their jelly coating. These three parts of the curve 

 may serve as convenient though general indices of the condition of the germ- 

 cells and indicate the period of ripeness, dying, and death of the eggs. This 

 statement applies only to such eggs whose jelly had not been removed by 

 mechanical or chemical means. 



Changes in Volume. 

 When the eggs of any female were carefully measured at different intervals 

 and the results plotted, the curve showed at least three points of special 

 interest. First, there was an initial period without change in the volume of 

 the eggs. This was followed by an unmistakable and continued increase in 

 size, followed by a third period during which, partly by budding off of 

 particles of the egg-cytoplasm and partly by fragmentation, and in extreme 

 cases more or less complete disintegration, the egg became decidedly smaller, 

 even smaller than its original size. These three parts of the curve correspond 

 with the three parts of the curve representing the disappearance of the egg- 

 jelly. And these three parts of the curve are associated with periods of 

 little or no aging, of rapid aging, and of the death of the eggs. This curve 

 of volumetric changes may be used as a much more accurate measure of the 

 rate and the extent of the effect of aging upon the egg than can the curve 

 for the egg-jelly. 



Effect of Temperature. 



If the processes involved in the aging and dying of eggs are chemico- 

 physical in their nature, wg should anticipate that Van't Hoff's law of the 

 proportionate increase in activity with a given change in temperature would 

 hold for the processes involved in aging eggs, and that the longevity was 

 proportional to the temperature at which the eggs were kept. 



The outline of a typical experiment may serve to make the matter clear. 

 Eggs of a female were kept in aliquot parts in several dishes of the same 

 type and size and with the same quantity of sea-water. One half of the 

 dishes were kept at a temperature, nearly constant, of 10° C, the other half 

 at a temperature of 27° to 29° C. At intervals the eggs were tested with fresh 

 sperm and the percentage of eggs that were fertilized in each batch was com- 

 pared and used as a measure of the differential mortality. The Van't Hoff 

 expectation was very closely realized. 



