Heredity in Protozoa 609 



In one case the sharply truncate form of the posterior end was 

 transmitted almost unchanged to the posterior progeny of the first 

 divisions, though the posterior half of the progeny was much longer 

 than in the parent. But in three more generations the posterior 

 individual, like all the others, had reached the normal form. 



d Anterior End with a Projecting Angle 



In a certain culture there occurred a number of individuals in 

 which the angle at the right of the anterior end was in a marked 

 degree longer than others. These Paramecia ran over the bot- 

 tom with the oblique surface of the anterior tip against the solid, 

 suggesting that the projecting angle was due to this action. The 

 angle disappeared in the changes connected with fission and did 

 not reappear in the progeny. 



e Crookedness or General Irregularity of Form 



A considerable number of cases were studied in which the body 

 of the progenitor was crooked, or was otherwise irregular in varied 

 ways. 



Such irregularities do not pass as such to the progeny. They 

 usually cause modifications in some or all of the progeny for sev- 

 eral generations, but these modifications are not repetitions of the 

 parent forms. They result from abnormalities in fission due to 

 the irregular form of the parent. Four categories of cases may be 

 distinguished : (i) Those in which the irregularity of the ancestor 

 induces in certain of the progeny various peculiarities that con- 

 tinue indefinitely; (2) those in which complete regulation finally 

 occurs, all the individuals returning, after a number of generations 

 to the normal form; (3) cases in which the result is to cause, in 

 some or all of the progeny, still greater irregularities, resulting 

 finally in monstrosities which cannot perform the vital functions 

 properly, and therefore die; (4) cases in which the irregular indi- 

 viduals do not reproduce at all; they persist for a time, and finally 

 die. Typical cases of each of these categories may be described. 



I The individual a, whose history has already been followed 

 (pp. 589-604), is an example of the first category. Here the crooked- 



