HALF AN HOUR WITH CORALLINES. 85 



which dwell in the cups are connected with each 

 other. 



These compound animals belong to the class 

 Hydrozoa, so named on account of their relationship 

 to the little Hydras of our fresh-water ponds. It 

 contains two orders, the members of both of which 

 live in British seas, and therefore are to be sought 

 for and found in beach rambles. The Hydrozoa are 

 remarkable for their peculiar specialization, notwith- 

 standing they appear such insignificant objects. 

 Each of the little animals living in the cups planted 

 at the joints or projections, is called a " zooid." 

 These have assigned to them as their duty the pro- 

 viding of the food for the colony. They possess no 

 reproductive powers whatever. In order to per- 

 petuate the species, therefore, a peculiar set of buds 

 are developed for this purpose. They are wholly 

 unlike their brethren of the same colony, for when 

 they are ripe and detached, they lead an entirely 

 independent existence, resembling jelly-fish. The 

 latter bring forth both ova and sperm-cells, and 

 these fructify and settle down to the plant-like 

 appearances of the " sea-firs " or corallines. 



Commencing with the first of these two orders, 

 the Corynida, we meet with the Tubularians, or 

 "Pipe Corallines." These are never prolonged to 

 form the little cups in which the polypites are con- 

 tained, the horny substance stopping short at their 

 bases. This is one of the distinguishing features 

 between the " Pipe Corallines " and the " sea-firs," 



