162 On the Geneiics of the Ciliate Protozoa 



84. The behaviour of a monstrous character during fission may be 

 illustrated by the abnormal race a of Jennings, which is fully described 

 for 22 generations. An abnormally bent organism divided into a normal 

 posterior daughter-individual and an anterior possessing a dorsal "spine." 

 In subsequent generations this spine persisted, passing sometimes to 

 the anterior, sometimes to the posterior individual. If we write A and 

 P for anterior and posterior individuals respectively, the transmission 

 of the spine for the 21 generations observed may be represented thus : 



APAPAPAPPPPAAAPAAPAAA. 



The last spined animal died. All the sister-individuals were normal, 

 save at the second generation. Here the anterior individual had a 

 small posterior ventral " tooth," which persisted for two further genera- 

 tions, passing each time to the posterior individual, and gradually 

 becoming smaller. At the next division it disappeared completely, 

 two normal individuals being formed. 



85. Jennings (1908) gives particulars of other abnormalities in 

 Paramecium and their behaviour during fission, with a long discussion 

 of his results. Special mention may be made of a curious " race " in 

 which the individuals showed a tendency to remain united instead of 

 separating comjjletely during fission. This race was " extinguished by 

 natural selection " in competition with free and more active organisms. 



86. McClendon (1909) obtained some results like those of Jennings 

 (§ 84), but in a different manner. As a consequence of centrifugiiig 

 some Paramecia^ he obtained an abnormal individual which divided 

 into two daughter-individuals each possessing a " hom." One of these 

 divided for 7, the other for 5 generations — the horn persisting and 

 passing to one of the daughter-individuals each time, the other being 

 invariably normal. Finally the horned animals died. In position and 

 size the horns differed in different organisms. " After each division 

 the horn is in a different position, and we can predict the position of 

 the horn in each generation by drawing an imaginary line bisecting the 

 animal in the preceding generation transversely." 



87. From the observations of Balbiani (§ 81), Simpson (§ 82), 

 Jennings (§ 84), and McClendon (§ 86), the following conclusions may, 

 I think, be drawn. Abnormal growths, however produced, in Para- 

 mecium may be mechanically handed on for a number of generations. 

 Whether they pass to the anterior or posterior product of division is 

 purely a matter of chance, depending upon the position which the 



' The species was P. caiidatum. 



