AGAMIC REPRODUCTION AND REJUVENESCEXCK 141 



Paramecium, the original mouth becomes, with more or less reorgani- 

 zation, the mouth of the posterior daughter individual and a new 

 mouth arises in the anterior individual, while in Slcntor the original 

 mouth and peristome remain as a part of the anterior individual 

 and the new peristome is that of the posterior individual. And, 

 finally, extensive developmental changes occur in the cytoplasm 

 before any visible nuclear changes. Evidently the process is more 

 than ordinary cell division. It is in fact an agamic reproduction 

 comparable to this form of reproduction in the multicellular forms, 

 and as such it exhibits characteristic features for each species and 

 involves much more extensive reconstitutional changes than cell 

 division. 



The data presented in chap, v and in the preceding sections of 

 the present chapter demonstrate that in at least many of the meta- 

 zoa a relation exists between reconstitution and rejuvenescence. 

 That being the case, the extensive reconstitutional changes involved 

 in fission in the ciUates make it at least probable that fission brings 

 about a greater or less degree of rejuvenescence. With this idea 

 in mind, the attempt has been made to determine whether appre- 

 ciable changes in susceptibility occur in connection with fission in 

 the ciliates. The forms tested thus far are Paramecium, Slcntor 

 coeruleus, a small form of Colpidium, and Urocentrum turbo, and the 

 results are essentially the same for all. The tests were made upon 

 actively dividing cultures reared from sterile infusions inoculated 

 with a few individuals. The rearing of pure line cultures was not 

 attempted, because definite results were obtained without this 

 procedure. 



In the early stages of fission no appreciable increase in suscepti- 

 bihty to cyanide has been observed. If any exists, it is not sufii- 

 ciently great to appear clearly in comparison with individual 

 differences in susceptibility. In pure line cultures some increase 

 in susceptibility in the earlier stages of fission might perhaps be 

 demonstrated. In the later stages of fission, however, when the 

 two daughter individuals are approaching separation and the recon- 

 stitutional changes are advanced, the susceptibility is distinctly 

 greater than in the single animals of approximately the same size 

 as the two members of the pair together. The possibility that the 



