102 ASSOCIATION OF ORGANISMS—THE WEB OF LIFE 
fact which has had much to do with the course of evolution in 
certain species. Reference should be made to vol. i, pp. 474-481, 
where some of the Colonial Zoophytes are figured and described, 
and also to vol. iii, pp. 327-328, for a brief account of the life- 
histories of such colonies. We are here only concerned with the 
characteristic features of colonial life, and it will be convenient to 
consider separately the two sub-groups of Sea-Flowers (Azthozoa) 
and Hydroids (//ydrozoa). 
Colonial Sea-Flowers (Anthozoa or Actinozoa).—To students 
of the British fauna the most familiar Sea- Flowers are the 
solitary forms known as Sea-Anemones, which abound on our 
shores. But in war- 
(Oa 
g mer parts of the globe 
SHR ie 
en fi Sy ~..,. Sorals are equally 
A 
abundant, and these 
may be either solitary 
or colonial. The 
former, or cup-corals, 
may be compared to 
anemones, but the 
lower part of the 
body is supported by 
a limy skeleton, while 
the latter may be re- 
garded as colonies of 
cup-corals, and present wide variations in shape, according to 
the mode of growth. In the majority of cases the members 
of the colony are all alike (fig. 1090), but this is not invariably 
the case. For in some of the Eight-rayed Sea-Flowers (Octac- 
tinia), e.g. the Sea-Pen (Pennatula), some of them are devoid of 
tentacles, and participate neither in active feeding nor in the 
production of egg-cells. Their special duty appears to be that 
of promoting breathing by setting up currents of sea-water which 
circulate through the fleshy substance of the colony. Ciliary 
action is the agency employed. 
[fydrowds (ff1ydrozoa).—The branching or encrusting colonies 
known as Hydroid Zoophytes exemplify division of labour more 
or less. As we have elsewhere seen, some of the individuals 
are specially concerned with egg-propagation, and these may be 
liberated as little free-swimming jelly-fish or medusz (see vol. iti, 
Fig. rogo.—Small Colony of a Coral (A strofdes calycularis) 
