324 GRACE MEDES 



longer treatment in producing reduction in size, while briefer 

 periods gave proportionally less marked results. 



In his later paper ('00) his earlier observations were con- 

 firmed, and additional ones on later stages showed that ''this 

 degree of reaction diminished in more or less regular proportion 

 from the time of impregnation onwards." So marked were his 

 results that he believed future research would reveal the justi- 

 fication for assuming this to be ''a general law of variation" not 

 only for temperature but also for other experimental conditions. 



He found that season affected growth in Strongylocentrotus, 

 a result which he ascribed to differences in maturity of the 

 eggs and sperms. During the period in which his experimental 

 work was done, namely, from the beginning of April until the 

 first of October, two maxima were obtained, one early in May 

 and one in September, with a minimum about the middle of 

 August. Impregnations made at this time resulted in 24.9 per 

 cent decrease in size below those made on the ninth day of May. 

 Observations on Spaerechinus supported, in the main, those 

 upon Strongylocentrotus, although in general the former were 

 less modified by changes in the environment. 



Driesch ('93), in his Entwicklungsmechanische Studien, gives 

 a brief table showing the more rapid development of the Spaere- 

 chinus embryos at increased temperature 31°, as compared 

 with a control culture at 19°. A difference, already apparent 

 at the two-cell stage, gradually increased during the succeeding 

 period until, at the time when the control had begun to show 

 a 'prismform' structure, the others were typical plutei with long 

 arms. 



Peter ('05) showed that the cells of Echinus and Spaerechinus, 

 under an increase of 10° in temperature, divided two and one- 

 half times as often, — an acceleration comparable to that of 

 chemical reactions at greater temperature. 



Marcus ('06) experimented with Strongylocentrotus lividus 

 and found a decided increase in rate of development in his 

 'Warmekultur' (22°) over that of the ' Zimmerkultur' (17° to 

 19°), and a still greater increase above the ' kaltekultur' (9°). 

 In the first the primary mesenchyme cells were approximately 



