THE AMERICAN MUSEUM JOURNAL 



slow creeping movement of the sea anemones and the umbrella mode of 

 propulsion peculiar to hydromedusse and the true jell yfishes — a beautiful 

 example of which (Dactylometra quinquecirra) is shown lazily swimming 

 near the broken pile in the group. But the polyps as a whole may be 

 considered as mere saclike stomachs, this specialization in digestion being 

 their most striking advance, aside from their multicellular structure, over 

 their protozoan progenitors. Yet there is good reason to believe that a 

 polyp-like condition such as this is ancestral to the structure of all the 

 higher and more complex groups of the Animal Kingdom. 



Associated with the sponges and polyps upon the wharf piles are many 

 other sedentary animals which like them feed upon the microorganisms of 

 the sea. At first glance these seem to be of hardly higher organization 

 than the polyps, but an examination of their structure at once shows them 



to be members of 

 much higher groups 

 in the scale of life. 

 Examples of these 

 are the edible bi- 

 valve mussels (Myti- 

 lus edulis) clustered 

 thickly upon the 

 piles. These ani- 

 mals are so closely 

 adapted to an at- 

 tached mode of life 

 and a diet of micro- 

 organisms that the 

 average observer, 

 unacquainted with 

 their affinities, would 

 fail to recognize 

 them as being in- 

 cluded in the same great phylum (Mollusca) as the active and highly 

 specialized squid, an example of which {Loligo pealii) is shown in the group 

 swimming near the same pile. Again, closely encrusting the pile to the left 

 are masses of coiled calcareous tubes, the homes of the tube-building worm 

 (Hydroides dianthus) whose multicolored gill circlets are everywhere peep- 

 ing forth from the tube-openings, giving their owners, to the superficial 

 glance, a much closer resemblance to hydroids and small sea anemones 

 than to highly specialized members of the annulate worm group to which 

 they really belong. 



Finally, everywhere on the piles are various species of sea squirts or 

 ascidians, singly and in colonies. These small saclike creatures each with 



The squid {Loligo pealii), a carnivorous free swininiing rnol- 

 lusk, propels itself by ejecting a stream of water. It has highly 

 specialized eyes and a beak-like mouth surrounded by sucker- 

 bearing tentacles 



