HYDROID CORALS. 5? 
Hydractinia echinata (Fig. 37) forms masses (each called a 
hydrophyton) encrusting shells. 
In Clava the reproductive buds remain permanently at. 
tached. It grows in pink masses on Fucoids, about half an 
inch high, and is very common on our shores. It is repre- 
sented in fresh water by Cordylophora lacustris Allman, 
which lives attached to rocks and plants in Europe and this 
country. 
Here comes in the group of Hydroids represented by 
Millepora and Stylaster, which were formerly considered to 
be Anthozoan corals. By the researches of L. Agassiz in 
1859, and H. M. Moseley 
in 1876, Millepora, which 
had been confounded 
with the coral polyps, 
has been proved to be a 
Hydroid allied, as Agas- 
siz stated, to Hydracti- 
nia. Like that Hydroid, 
it forms a calcareous 
encrusting mass, but of 
much greater extent, a 
considerable proportion 
of the coral in the Flori- 
da reefs being formed 
by the Millepora. Our pig 99 sauepora nodosa. 
. < 6 , a, nutritive 
American species is Mil- zooid ; 2, tentaculated zooid ; ¢, lasso-cell ; @, 
i ‘ ; the same coiled up in its cell ; ¢, a third form. 
lepora alcicornis Linn., 
while our description is taken from Moseley’s account of 
Millepora nodosa Esper. (Fig. 38). Its generic name is de- 
rived from the numerous pores or calicles dotting its surface 
and arranged in irregular circular groups, consisting of a 
central calicle, or cup-like hollow, with from five to eight 
smaller calicles arranged around it. The mass of the coral, 
or hydrophyton, consists of fibres (canals or tubes) of lime, 
forming a spongy mass, traversed in all directions by tor- 
tuous spaces which ‘‘ form regular branching systems with 
main trunks, giving off numerous branches, from which 
arise secondary branches, and from these again smaller 
