130 



THE SEA SHORE 



the horny skeletons of colonies of crelenterates of the simplest type, 

 belonging to the division Hydrozoa. 



If we examine them with a lens we find that there are little cup- 

 like bodies projecting from each portion or branch of the stem-like 

 structure, and that the stem itself is hollow, with a communicating 

 pore at the base of each cup. This constitutes the skeleton only of 



FIG. 80. Sertularia cupressina 



the colony the dead matter, so to speak, which persists after the 

 living creatures have perished ; but if the specimens collected have 

 been obtained fresh from the sea, placed in a glass of sea water, and 

 then examined with the aid of a lens, little jelly-like hydroids or 

 polypites will be seen to protrude from the cups, and extend their 

 short arms in search of food. 



