254 



THE EVOLUTION THEOKY 



unicellular animals probably seems to us simpler and more homogeneous 

 than it really is. Among Infusorians it is quite obvious that inheri- 

 tance implies more than the mere halving of the mother-animal into 

 the two daughter-cells ; something more must be involved. For among 

 these unicellular animals the differentiation of the body is not only 

 great, but it is unsymmetrical. The posterior and the anterior ends 

 are different, and the transverse division of the animal, in which the 

 process of reproduction here consists, does not produce two halves, 

 but two very unequal portions. In the division of Stentor, the 

 so-called trumpet-animalcule (Fig. 60), the anterior portion contains 



Fig. 60. Stentor rtcselii, trumpet-animalcule. Process 

 of division, wsp, ciliated spiral leading to the mouth 

 (m) ; c«, contractile vacuole. A, in preparation for 

 division, the nucleus {k) has coalesced into a long twisted 

 band. B, a second ciliated spiral (wsp') has begun to 

 be formed ; the nucleus (fc) is contracted. C, just before 

 the constricting off of the two daughter-Stentors. 

 Magnified about 400 times. After Stein. 



the funnel-shaped mouth and gullet with its complicated nutritive 

 apparatus, the circular peristome with its spirally curved rows of com- 

 posite ciliated plates, the so-called membranellse, and so forth; the 

 posterior half contains nothing of all this, but possesses the foot of the 

 mother-Stentor with its attaching organ, which the anterior half lacks. 

 But each of the two portions possesses the power of ' regeneration,' 

 that is, it is able to develop anew the missing parts, mouth or foot, 

 and so on. So that here there is no longer merely a simple continu- 

 ance of the maternal organization in the daughter-animals, there is 



