592 H. S. yenjTings 



anterior product a^-\ while the larger projection was at the ante- 

 rior end of the posterior individual a^*-. In the period just before 

 and after the separation of the two parts (which occurred at 10.55) 

 this larger projection grew rapidly still larger, longer and sharper, 

 as if it were being pushed out under pressure. Immediately after 

 division the posterior product a'^-^ had the form shown in Fig. 3, S 

 the projecting spine being as long as the body was thick, and 

 situated on the aboral side, nearly at the anterior end. 



Now this posterior individual a^'^ began to grow rapidly. 

 Growth was most rapid at the anterior tip; this pushed out so as 

 to leave the spine at some distance from the anterior end. The 

 spine itself became still longer and stouter. At the same time 

 the entire body increased in length, the growth seeming most 

 rapid at the anterior end and decreasing toward the rear. Twenty 

 minutes after division the posterior individual a^'^ had the form 

 shown in Fig. 3, ^. 



The change of form now continued much more slowly, so that 

 at the end of four hours the shape was that shown in Fig. 3, ®. 



In the anterior individual («''0 a parallel process of growth 

 occurred; the anterior part of the body pushed out rapidly, while 

 the posterior part merely changed shape a certain amount. The 

 small projection was thus left near the posterior end, on the oral 

 surface (Fig. 3, ^). 



Thus we have now on each of these individuals a definite new 

 structure, the origin of which we know, while the animals are 

 quite normal in other respects. The new structures have arisen 

 during the reproductive processes — at a period comparable, if 

 there is any such in the life of the infusorian, to the germ cell 

 period, just before development begins, in a Metazoan. Tower 

 ('06) found that in certain Metazoa changes wrought in the organ- 

 ism at this stage of its life give rise to permanent inherited modi- 

 fications, though environmental eff'ects at other stages are not 

 inherited. We have then perhaps as favorable a case for studying 

 the transmission of a suddenly produced new structure as we could 

 expect to find in the Protozoa. 



We shall here follow only the history of the large anterior spine, 

 in a^-^ (Fig. 3, ^), taking up later the fate of the short tooth in a^'K 



