224 



LECTURES ON BIOLOGY 



bears the mouth-aperture to which leads a long ciliated wreath, the 

 ' adoral cilia-zone ' ; the pointed posterior end is furnished with a 

 suctorial disc. 



Let us now suppose that Stentor begins to draw itself out. 

 What would happen ? We should have two halves, of which 

 one would be without a mouth-aperture and the * adoral ciliated 

 spiral,' whilst the other would be without the suctorial foot. 

 But Nature could not be so unjust as to endow both individuals 

 with unequal proportion. When a Ciliate therefore feels that it has 

 become too large for one animalcule it begins to lay down its most 

 important organella in duplicate. It is no longer content to double 

 only its nucleus but forms, as, for instance, in Stentor, a second 

 ciliated wreath and a new mouth-aperture below the old. Division 

 only takes place after this has been done, and now the two young 

 Stentors resemble the mother in everything except in size and 

 unimportant details. 



It is possible to multiply the Ciliates 

 artificially by dissection. As long as 

 these individual sections have obtained 

 their share of nuclear substance they 

 are always able to survive the operation, 

 and shortly to regenerate the absent 

 organella. Thus a Stentor may easily 

 be cut into two, three, four, or more 

 parts, and each section will grow again 

 into an adult animalcule if the condi- 

 tions are at all favourable (see fig. 55). 



The fertility of most unicellular 

 organisms is astonishing. After a few 

 months we would find in our Para- 

 weeciww-culture a succession of hun- 

 dreds of generations. If we discon- 

 tinued our observations at that period 



we should gather the impression that reproduction by fission 

 proceeds here until all eternity, apparently as undisturbed and 

 uniform as in the Arnosba. But further observation teaches us 

 that this does not apply to the Ciliates without considerable 

 modifications. 



After multiplication has proceeded for some time normally 



FIG. 55. Stentor cceruleus. 



(1) Cut into three nucleated 



parts ; (2) Three Stentores 



produced by regeneration. 



