Heredity in Protozoa 



605 



the history of the large spine of a^" and its descendants. We will 

 now follow briefly that of the short posterior spine of a^-HFig.S/). 



The next division (night of May 7) was of course at about the 

 middle of the body, so that the anterior product a}-^'^ was a normal 

 individual without a spine. The posterior product a}-^-^ had the 

 spine in about the same position as in the previous generation, 

 though it shifted during growth a little farther forward (Fig. 8, ^). 



At the next (fourth) division the point passed to the posterior 

 product (<3^-^-^-^) and remained in nearly the same position as before 

 (Fig. 8, ^). It had become smaller, so that it was now a mere 

 lump, hardly noticeable. 



Fig. 8 Diagram of the history of the small tooth in the race a. See test. 



At the next fission (fifth) the point or lump quite disappeared, 

 being in some way reduced during the growth processes accom- 

 panying division. Both individuals resulting from fission were 

 of the normal form (Fig. 8, "*). 



Thus this small posterior point persisted through but three gen- 

 erations, and in each generation it was found in but one individual. 

 A process of regulation of form took place slowly, accompanying 

 the changes involved in fission, till finally the new structure had 

 disappeared. 



