28 TIIE DOCTRINE OF DESCENT, 
exists, without taking account of the scale by which it 
rises or sinks. This standard will, however, soon be made 
manifest 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, a layer of muscles, and a supporting 
membrane, which gives consistency to the whole, and 
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 animalcule 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, 
