MARINE BIOLOGICAL STATION AT PORT ERIN. 83 



have a rooted plant-like appearance. But although rooted 

 and branched, and known as animal-plants (Zoophytes), it 

 must be remembered that these colonies are true animals, 

 and are moreover not the lowest animals, or those nearest 

 to plants, but are distinctly higher than the Protozoa and 

 the Sponges. A piece of one of the " Sea-firs," or Sertu- 

 larian Zoophytes, is shown, natural size, at 3 (Sertularia 

 abietina), where each of the little angular enlargements or 

 projections on the stem and branches is a horny cup con- 

 taining one of the members of the colony. Another 

 Sertularian Zoophyte (Sertularella polyzonias) is seen 

 enlarged in the living condition, under the microscope, 

 at 1. The little members of the colony (the Zooids) are 

 seen protruded from their delicate horny cases. Each has 

 an open mouth surrounded by about 20 delicate filaments, 

 the tentacles, by means of which the Zooid catches food 

 from the surrounding water. Each such Zooid is very 

 similar in structure and appearance to the little fresh- 

 water Hydra, and consequently these colonies are 

 frequently called " Iiydroid Zoophytes." 



Another common and closely related kind of Iiydroid 

 Zoophyte (Ohelia geniculata) is seen at 2. This is called a 

 " Campanularian " Zoophyte because each cup containing 

 a Zooid is bell-shaped and placed at the end of a ringed 

 twig or handle. This figure also shows certain larger 

 cases, in which are formed special buds that become 

 detached as little glassy bells or jelly-fishes for the 

 purpose of producing and scattering the eggs that will 

 eventually give rise to new colonies. The fixed Hydroid 

 Zoophyte thus gives rise by budding to free-swimming 

 Medusae (like that shown at 10, fig. XII.) ; and the 

 Medusa in turn produces eggs which give rise to fixed 

 Zoophytes. Such a life-history is an example of 

 " alternation of generations." 



