COBAL-FOBMING HTDR0ID8, 
23 
eral round sacs, or ^^medusa-buds" which produce either 
male or female medusae. These medusa-buds are like the 
free medusae of Coryne. The marine Hydroids, then, are 
Fig. 20.— Animal of Millepora nodosa, a, nutritive zooid; 6, reproductive 
zooid ; c, lasso-cell ; d, the same coiled up in its cell ; a third form. All 
highly magnified. 
usually of distinct sexes, growing by colonies, which are 
either male or female. 
The minute animals of Millepof^a 
secrete large coral-like masses on the 
reefs of Florida and the Pacific Ocean. 
The name is derived from the num- , 
berless minute holes or pores scattered 
over the surface in which the nutritive 
(Fig. 20, a) and reproductive zooids 
(Fig. 20, b) live. On breaking off pieces 
of the living coral one's hand is stung 
and made sore for days by the stings 
from the lasso-cells, so poisonous is this 
coral-like growth (Fig. 20, c, d, e), 
A common Hydroid on our north- Fig. 21. 
em shores is the Coryne (Fig. 21), 
which differs from the foregoing kinds 
in producing a free bell-like form called a medusa or 
-Polypite of Co- 
ryne mirabilis, with 
a medusa-bud at a. 
Much enlarged. 
