VEGETATIVE PROPAGATION 



319 



p.v.-{-0 



Weismann, the products of this division later on divide in their 

 turn, and so on indefinitely. And it is upon this belief that the 

 distinguished zoologist in question founds his doctrine of the 

 "immortality of the Protozoa", which involves the statement 

 that death by " natural causes ", as a coroner would put it, is 

 unknown among Animalcules. But at present we do not know 

 definitely whether or no divi- 

 sion can go on for an inde- 

 finite number of generations, 

 as Weismann's doctrine pos- 

 tulates. 



We may take as further 

 illustrationsof fission(fig. 844) 

 the Trumpet - Animalcule 

 [Stentor) and the Bell-Ani- 

 malcule ( Vorticella), both of 

 which are much more highly 

 organized than Amoeba, and 

 belong to the group of Ciliata, 

 in which the body is pro- 

 vided with cilia, i.e. short 

 threads of protoplasm ca- 

 pable of movement. The 

 Trumpet- Animalcule is elon- 

 gated in form, with a narrow 

 attached end, and a much 

 broader free end, provided 



with a snort spiral 01 cilia, a and b, stages in transverse division of Trumpet-Animalcule 



1 "U ' t., Cf^r^A \^c^ -> ' rv /-> t- [Steiitor); ;;2, mouth; ?^, nucleus; p.v., pulsating vacuole, c, D, 



Dy WniCn lOOU-Dearmg cur- stages in equal longlmdinal fission of Bell- Animalcule (Korz'/- 



rentS are set Un in the SUr- '^^^^^)' ^"^ E- repeated unequal longitudinal fission of same. 



V N, Large nucleus; k, small nucleus; p.v., pulsating vacuole. 



rounding water. The nu- 

 cleus is elongated, and shaped something like a string of beads. 

 Fission is here transverse, and though each half takes its share 

 of the nucleus, one of the new individuals is constituted by the 

 broad end and the other by the narrow end of the original body. 

 This is of no great moment, as each of them develops the parts 

 which it lacks before separation is completed. 



In the Bell -Animalcule fission is longitudinal, so that there 

 is a fairer division of the parent Animalcule between the halves. 

 One, however, keeps the stalk, which does not split, while the 



Fig. 844.— Fission of Ciliated Animalcules, enlarged 



