246 
IOWA ACADEMY OF SCIENCE Voi,. XXVII, 1920 
fairly definite growth-forms; while such diffuse colonies as 
Cyathophyllum calvini and species of Diphyphyllum have appar- 
ently neither definite shape nor definite size, and one colony of 
Cyathophyllum calvini has been found which is reported as having 
probably had a diameter of fifty feet or more. 
CONCEUSIONS 
Two points seem clear : first, there has been progress throughout 
the geological history of corals from solitary to colonial, and 
within the colonial corals progress in compactness; second, the 
most successful of modern corals are those which have the highest 
degree of colonialism. Since this is so, there must be definite 
advantages in sociality. 
In the animal kingdom there is always an advantage in numbers. 
The colonial condition supports a greater number of individuals 
in a favorable environment than is possible in the solitary condi- 
tion. There is moreover an economy of skeletal tissue, for in- 
stance, epitheca. Then too, asexual multiplication, by budding 
and by fission, is more economical than sexual reproduction 
because in the former case the young inherit the same environment 
which has proven favorable for the parent and enjoy the pro- 
tection of the parent polyp and of the colony. This is the same 
principle which in higher animals is called care of the young. 
These advantages are true not only of coral heads entirely cov- 
ered with soft parts but also of colonies bearing only isolated 
polyps. In colonies where there is continuation of soft parts, 
and especially confluence of visceral chambers, there are the 
further advantages of equal distribution of food and transmission 
of nerve impulses. Where visceral chambers are continuous food 
ingested by one polyp will be transmitted to others ; and continuity 
of soft parts means possibility of transmission of impulses from 
polyp to polyp, so that food and warning-stimuli call forth an- 
ticipatory reactions in neighboring polyps. 
These advantages — community of food supply, economy of 
space, protection of young, transmission of warning stimuli, 
common action against enemies, and protection against extinction 
aflPorded by a large number of individuals — characteristic of all 
social groups in a certain stage of their evolution, are found to 
be present therefore even in the primitive sociality of the Madre- 
poraria. 
