ECOLOGICAL 115 



of types that may be found in a true society of many individuals, 

 such as a community of white ants, of which Maeterlinck has 

 written so interpretatively. 



The formation of colonies finds very varied expression among 

 the Ccelentera (all or mostly stinging animals), such as zoophytes, 

 Siphonophores, and sea-pens; but it recurs at a higher level in the 

 Polyzoa or Bryozoa, where again there may be remarkable division 

 of labour. It is seen also in a remarkable type called Cephalodiscus, 

 which lies near the border-line between Invertebrates and Verte- 

 brates. In this type the individuals composing the colony are not 

 connected to one another save by a common investment; yet in 

 the possibly related Rhabdopleura, another very remarkable animal, 

 the individuals are united by a common stolon. The highest reach of 

 such united colony-formation is found among the Tunicates, and 

 while the majority are fixed and often beautifully grouped, there 

 are some free-swimming types, such as the brilliantly luminescent 

 "Fire-flame" or Pyrosome, which may be as long as one's arm. In 

 many of these "social" Tunicate groupings the individuals (formed 

 by budding) have separate inhalant orifices but share an exhalant 

 orifice with a group of neighbours, or, as in the Pjnrosome, with all 

 the members of the colony. 



The gradations in animal colonies are instructive, (i) A complex 

 sponge may be formed by the fusion of numerous budded individuals, 

 but it is rather an imperfectly integrated body than a colony. 

 The individuals lose their distinctness and coalesce. The various 

 parts or regions of the big body do not always work together in 

 harmonious interdependence. A large portion may be cut off without 

 making any difference. A living bath sponge may be cut up and 

 bedded out. In fact, there is practically no division of labour, and 

 there is no trace of a nervous system, not even of nerve-cells. (2) A 

 level not much higher is represented by the huge masses of "brain- 

 coral" and some of the other reef -builders. There may be indistinct 

 delimitation between adjacent polyps, which arise by budding or 

 by fission. Thus one polyp may produce another with a separate 

 mouth, tentacles, and gullet, but sharing a common gastric cavity. 

 But nerve impulses can pass from one part of the colony to another 

 by networks of nerve-cells. Integration is beginning. (3) In most 

 Alcyonarian corals each member of the colony is complete in itself, 

 but cdl are connected by canals, and it is characteristic of the Alcy- 

 onarians, as contrasted with reef-building Madrepores, that a new 

 individual is not directly budded off from an older one, but arises 

 indirectly from a canal or stolon. (4) Slightly higher on this inclined 

 plane are the dimorphic Alcyonarian colonies. (5) Worthy of a 

 separate level are some of the Pennatulids or sea-pens which can 

 move as a whole. They are not fixed to the substratum, but have 

 their basal end freely embedded in the mud, and they are able to 



