6 



ANTHOZOA HYDROIDA. 



fairy forest peopled with its myriads of busy polypes, while 

 the Sertularia pumila rather loves the more common and 

 coarser wracks. The choice may in part be dependant on 

 their habits, for such as are destined to live in shallow water, 

 or on a shore exposed by the reflux of every tide, are in 

 general vegetable parasites; while the species which spring 

 up in the deep seas must select between rocks, corallines or 

 shells, the depths at which they are found being too great for 

 the vegetation of sea- weed.* The more robust tribes grow 

 erect, and, being flexible and elastic, yield readily to the waves 

 and currents ; but some of the very delicate species avoid a 

 shock for which they are unequal, by creeping along the sur- 

 face. 



A very few of these zoophytes are naked, but in the ma- 

 jority the soft body is invested with a horny sheath that is 



called the polypidom. 



Fig. 2. This offers us many 



specifical varieties, and, 

 in general, is confer- 

 void and more or less 

 divided, the ramifica- 

 tions being disposed in 

 a variety of elegant 

 plant-like forms. The 

 stem and branches are 

 alike in texture, slen- 

 der, horny, fistular,and 

 almost always jointed 

 at short and regular 

 intervals, the joint be- 

 ing a mere break in 

 the continuity of the 

 sheath without any cha- 

 racter of a proper hinge, 

 and evidently formed 

 by regular periodical interruptions in the growth of the 

 polypidoms. Along the sides of these, or at their extremi- 



* Lamouroux says, "We find some polypidoms placed always on the southern 

 slopes of rocks, and never on that towards the east, west, or north. Others, on the 





