28 THE DOCTRINE OF DESCENT. 



exists, without taking account of the scale by which it rises 

 or sinks. This standard will, however, soon be made mani- 

 fest by the comparison of a lower with a higher animal. 

 Let us select the fresh-water polype and the bee. 



The little animal, several lines in length, which in our 

 waters usually lives adhering to a plant, is a hollow 

 cylinder, of which the body-wall is formed of two layers 

 of cells. The external layer gives rise to fibres which 

 act as muscles, and to a supporting membrane which 

 may be compared to a skeleton. The mouth is sur- 

 rounded by arms of similar construction, and varying in 

 number from four to six. The surface of the body is 

 studded with numerous little stinging vesicles, which 

 by their contact stun any smaller animalculae straying 

 within the reach of the polype, and render them an 

 easy prey. This is, in a few words, the construction of 

 the animal. It possesses no arterial system, no special 

 respiratory apparatus ; the functions of the nerves and 

 the sensory organs are performed by the individual parts 

 of the surface. Reproduction is usually effected by the 

 budding of gemmules, which fall off at maturity, but 

 occasionally also by the produce of very simple sexual 

 organs. 



On the other hand, hours do not suffice to describe 

 the structure of a bee. Even externally, its body, 

 which possesses so highly complicated a structure, pro- 

 mises a rich development of the interior. The man- 

 ducatory apparatus can be rendered comprehensible 

 only by comparison with the oral organs of the whole 

 insect world. The various divisions of the alimentary 

 canal are each provided with special glands. The rich 

 psychical life, all the actions which imply intelligence, 



