CORAL-FORMINQ HTDROIDS. 



23 



eral round sacs, or "medusa-buds" which produce either 

 male or female medusas. 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 

 »ooid; c, lasso-cell; d, the same coiled up in its cell; e, a third form. All 

 highly magnified. 



usually of distinct sexes, growing by colonies, which are 

 either male or female. 



The minute animals of Millepora 

 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.— Poiypite of Co- 



^ ^ .p-,. , ryne mirabilts, with 



ern shores is the Coryne (rig- -il), a medusa-bud at a. 



which differs from the foregoing kinds "'' ™ '^'^^'^ ' 



in producing a free bell-like form called a medusa or 



