Heredity in Protozoa 593 



Fourth generation. We left the individual with the long ante- 

 rior spine in the condition shown in Fig. 3, ^. At the next fission 

 (night of May 4) the spine remained with the anterior product 

 a^'-'^, while the posterior product a^'^'^ was a typical individual 

 without a spine. In this fourth generation, since the division 

 had taken place at the middle and there was subsequent outgrowth 

 of the anterior tip, the spine was left behind the middle of the new 

 individual (Fig. 3, ^). The spine itself had become still longer 

 and more slender. In structure it was a tube of ectosarc enclos- 

 ing a narrow canal filled with endosarc. It was flexible, bending 

 readily when it came in contact with obstacles, but it did not 

 show active movements. 



Fifth generation. At the next division (noon, May 6) the plane 

 of division lay just in front of the base of the spine, so that the 

 latter went to the posterior individual (a^*^'^'^), and was situated 

 at its anterior end (Fig. 3, ^). The other (anterior) individual 

 (<3i-2-i-i) was normal, as usual. In the process of growth, consist- 

 ing largely in the pushing out of the anterior end, the spine came 

 to lie farther back than at first, so that in the adult infusorian 

 it was a little in front of the middle (Fig. 3, ^). The spine had 

 become slightly enlarged at its tip, and bent to the right at about 

 its middle. 



Sixth generation. The plane of the next division (night of May 

 6) passed just behind the spine, so that the latter was now left on 

 the anterior specimen, a^*-"^'-"^, while the posterior specimen was 

 normal. The spine was now bent near the base, so as to extend 

 backward parallel with the body axis (Fig. 4, "). 



Seventh generation. At the next division (night of May 7), the 

 spine of course went to the posterior individual, ^^•-■^■-■^■-(Fig. 4, ''). 

 It was situated a trifle in front of the middle of the body. The 

 spine was now long and curved downward and backward over the 

 right side of the animal. Its base was much broader than before, 

 and a shorter spine had pushed out forward from the angle between 

 the base of the spine and its main body. 



Eighth generation. At the next division (night of May 8), the 

 spine went to the anterior individual (^i-2-i-2-i-2. 1^ ^j^j ^^g situated 

 very nearly at its posterior end, though a little displaced toward 



