VEGETATIVE PROPAGATION 



323 



a rounded shape, cilia appear on its surface, and the size and 

 shape of the adult are gradually attained. 



Conjugation of Animalcules. The vegetative propagation of 

 Animalcules is commonly promoted by, and often dependent upon, 

 a remarkable process to which the name of conjugation has been 

 applied. This has been very carefully studied in some of the 

 ciliated forms, as, e.g., in the Slipper- Animalcule (Paramcecium) 

 and Bell-Animalcule ( Vorticella), which will serve as our illus- 



Fig. 847. Temporary Conjugation of a Slipper-Animalcule (Paramcecium caudatum}, diagrammatic and enlarged 



A, A free individual; N, macronucleus; n, micronucleus. B-F, Stages in conjugation, showing successive 

 divisions of micronuclei (macronuclei omitted), the fragments which disappear represented by clear circles in 

 E the active nucleus (a) of each individual is migrating towards the passive nucleus (p] of the other individual 

 in F each individual contains a compound nucleus. G-N, Changes in a conjugated individual leading to 

 transverse fission, followed by (o, P) a further division in each half. 



trations, though minute details will not be given, as the process 

 is very complicated. 



Within the body of one kind of Slipper-Animalcule (Para- 

 mcecium caudatum, fig. 847) two specialized particles of proto- 

 plasm can be seen, placed close to each other. The larger is 

 the macronucleus, but it is with the smaller, or micronucleus, that 

 we are here principally concerned. During conjugation two indi- 

 viduals apply themselves closely together, and remarkable changes 

 take place in the nuclear structures. The macronucleus gradually 

 disintegrates and disappears, but the micronucleus, by two suc- 

 cessive divisions, is converted into four fragments, of which three 

 break down and disappear. But the fourth fragment divides once 

 more, and the fates of its halves differ. We may term them the 



