262 RALPH S. LILLIE. 



process may show a very rapid acceleration through a range of a 

 few degrees above the critical temperature; it is then clear that 

 the change of temperature acts in some other way than simply 

 by accelerating an already existing chemical reaction. This is 

 the class of cases to which belongs the influence of higher tem- 

 peratures in initiating development in starfish eggs. Such 

 departures from the usual temperature-coefficients of physio- 

 logical processes indicate the entrance of other factors, the nature 

 of which may be partly inferred from the character of the tem- 

 perature-coefficient. Thus, to take the case of the starfish egg: 

 in order to induce development of all eggs to a larval stage by 

 exposure to a temperature of 31° it is necessary to keep them 

 at this temperature for a period of about 15 minutes; at 36° an 

 exposure of only one minute is necessary. The physiological 

 process, whatever its nature, which renders the egg capable of 

 proceeding with its development, thus takes place about fifteen 

 times as rapidly at 36° as at 31°. This high temperature- 

 coefficient indicates that a physical rather than a purely chemical 

 change — possibly a change of the same nature as that determin- 

 ing the liquefaction of a warmed gel — is responsible for the 

 altered behavior of the egg. The time-relations show that some 

 definite and progressive process, the end-effect of which is to 

 remove the conditions hindering further development, is taking 

 place in the egg during the entire 15 minutes at 31°. Exposure 

 for the full period of fifteen minutes is necessary to bring this 

 process to its completion, i. e., to a stage at which the egg is 

 in a position, when returned to sea-water, to continue auto- 

 matically its development to a larval stage. If the exposure is 

 only 5 minutes there is also a definite change in the egg; a 

 typical fertilization-membrane is formed and there may be 

 some irregular change of form or possibly a few abnormal 

 cleavages, but the egg never develops far and soon dies. In this 

 case the process of activation is evidently incomplete, and only 

 a few of the early steps in development are carried out. If the 

 exposure is too long (20 to 25 minutes) the egg also fails to 

 develop; the process initiated by the higher temperature thus 



excitation of thermal sense-organs (e.g., of frog's foot) and of certain vaso-motor 

 and other temperature-regulatory mechanisms by heat; thermotactic responses. 



