306 E. G. Spauldtng 



all stronger; continued in all weaker solutions. Second cleavage 

 stopped by 10 cc. sugar sol. plus 13.75 ^^- ^' ^•■> P^^^ ^^ ^^•' ^^ 

 third by 10 cc. sugar, plus 15 cc. s. w. plus i^; the fourth, by 10 cc. 

 sugar plus 16.5 plus 1.5 cc. s. w. 



Experiment II, July 21: Made for purposes of refinement; 

 found to be confirmatory of preceding. 



Experiment III, July 22: First segmentation stopped by 15 

 cc. sugar plus between 16 and 18 cc. s. w. plus i^ cc. 



Experiment IV, July 22: Inhibition point found to be between 

 16 and 16.5 cc. s. w. plus 15 cc. sugar plus i^ s. w. 



Experiment V, July 24: First cleavage stopped by 15 cc. sugar 

 plus \ (16 plus 16.5) cc. s. w. plus i^ cc. This means that the (16), 

 and all stronger, stopped, while the (16.5) and all "up" from this 

 "allowed to proceed." This method of taking the "intermediate 

 point" was subsequently adopted in each case. Second segmenta- 

 tion stopped by 15 cc. sugar plus ^ (20.5+21) s. w. plus i^ cc; 

 third, by 15 plus h (21.5 +22.5) plus ih cc. 



Experiment VI, July 27: Temperature 23.5 C. Fine lot of 

 eggs. Fertilized at li a. m.; repeatedly and frequently observed 

 up to 3 p. m.; observations all confirmatory. First segmentation 

 stopped by solution 15 cc. § mol. sugar sol. plus 16.75 ^^- ^- "^- P^^^ 

 1.5 s. w.; second by 15 cc. sugar plus 20.75 plus 1.5 cc. s. w.; third 

 by 15 cc. sugar plus 21.5 plus 1.5 cc. s. w. Control; over 95 per 

 cent of the eggs segmented uniformly. 



For the purposes of the computation to be made, the surfaces 

 and volumes of each stage must be found. This w^as done as fol- 

 lows. In the one-cell stage the typical or "modal" sea-urchin 

 egg is approximately spherical; accordingly the diameters of as 

 large a number as the period of 55 to 60 minutes elapsing before 

 the first segmentation allowed were measured by means of an 

 ocular micrometer; from these data, widely divergent values being 

 excluded, the average diameter was found, and the surface and vol- 

 ume computed from well-known formulae. In the two-cell stage 

 the typical form is that of two oblate ellipsoids; the long and the 

 short axis of each ellipse was accordingly measured for a number 

 of eggs, the average for each taken, and the surface and volume 

 computed. Difficulties in doing this for the four and eight-cell 



