(12) 



pipette, outlined with the camera lucida, and transferred 

 to a new culture slide. 



Records were kept on small sheets of paper, each of 

 which contained the number of a given individual, the date 

 upon which it was isolated, its camera outlirie, and the 

 numbers and dates of isolation of all of its progeny. 

 Later, during the process of working up the data, the 

 spine number and certain measurements of the outline drawing 

 were added. Since these drawings, made from the living 

 organism while the new shell was still clean and translu- 

 cent, gave all the data required, no attempt was made to 

 preserve the shells of individuals when they died or were 

 discarded . 



In some of the later work, when attention was centred 

 wholly on the inheritance of spine number, the records were 

 much less elaborate, consisting m.erely of the number of the 

 specimen, the date on which it was isolated, its spine num- 

 ber, and the corresponding data for all of its offspring. 



Statistical methods and use of terms. The follo'wing 

 measurements were taken on each of the camera outlines. 

 Diameter of shell and mouth in the "antero-posterior" axis. 

 Diameter of shell and mouth in an axis at right angles to 

 the "antero-posterior" axis. To secure a number proportional 

 to the area of the shell, the two diameters were multiplied 

 together. This was called the "shell size index". In order 

 to obtain a nujrber related in some way to the form of the 

 shell, the "antero-posterior" diameter was divided by the 

 other diameter. This was called the "shell form ratio". 



