288 LIFE : OUTLINES OF GENERAL BIOLOGY 



cerned : necessary though it be for the cell's protection, the plant's 

 coherence, water-passage, etc. So when we bum our wood, we 

 warmly realise how much fuller is our animal oxidation, how great 

 the gain to our animal energies and activities accordingly. 



REGULATIVE SYSTEM 



INTEGRATION. — Sponges are animals which often show detailed 

 complexity, e.g. in their water-canal system, their component cells, 

 and their loose spicules or coherent skeleton; but they have a 

 minimum of integration. That is to say, the body is but slightly 

 unified; a large piece can be cut off without making any appreciable 

 difference; and it may be noted that sponges have no specialised 

 nerve-cells at all. Around the larger exhalant openings or oscula 

 there are in some cases unstriped muscle-cells which contract when 

 touched, and might therefore be called neuro-muscular — receptors 

 and effectors in one, but there are no nerve-cells — a fatal defect, 

 prohibiting integration. In an animal at a much higher level, the 

 Portuguese Man-of-War (Physalia), a colony of transformed medu- 

 soid individuals, sometimes of at least five different kinds, there is 

 unified movement; the various "swimming-bells" work in harmony, 

 being regulated by a network of nerve-cells extending through the 

 colony. Yet there is no central nervous system, and many members 

 of the colony can be cut away without any appreciable damage 

 to the life of the whole. In the great majority of animals, however, 

 from earthworm to elephant, from bee to bird, we have to do not 

 only with differentiation or division of labour in various degrees, 

 but with an increasingly unified control or regulation of the life 

 of the body which is called integration. When we say that one 

 animal is "higher" than another, we mean that it is more differen- 

 tiated and also more integrated. 



Some measure of integration is implied in the physical binding 

 together of the body, for instance, by the possession of a dorsal axis 

 or backbone to which the limbs are usually attached; or by the 

 grouping of the muscles, which often work together in contrasted 

 harmony like the biceps and the triceps of the forearm, the one 

 relaxing as the other contracts. The same result may be reached 

 by the possession of a coherent carapace or shell, as in crab or 

 snail, to which some of the muscles of the animal are intimately 

 attached. In various ways, then, there is brought about a measure 

 of physical integration. 



Much more important, however, is the integrative influence of 

 the nervous system, of which we have already spoken. This is 

 increasingly integrative (a) in proportion as the nerve-ftbres reach 

 to every part of the body, even the most outlying, and (6) in pro- 



