214 ZOOLOGY 



war v (Physalia, 1 Fig. 192), which often swarms in the 

 Gulf Stream. The huge float which lies on the surface 

 of the water serves also as a sail by which the animal is 

 transported by the wind. There are other smaller, more 

 graceful species of more typical form (Fig. 201). The 

 structure of a siphonophore is very complex. From the 

 float hangs a central stem. Upon this stem are budded 

 feeding zooids hydranth-like forms provided with mouth 

 and tentacles and reproductive zooids- - gonophore-like 

 forms which produce the germ cells. There are leaf -like 

 expansions also, which are rudimentary medusae. All the 

 many forms budded on the stem are modifications of the 

 hydroid type. 



Contrasted with the Hydrozoa are the Scyphozoa, 2 which 

 are, on the whole, larger animals. These, too, occur both 

 in the sessile, polyp form and in the jelly-fish form. The 

 sea-anemones are common examples of the polyp. These 

 are, for the most part, solitary, fleshy creatures, often 

 brilliantly colored, and therefore appropriately called by 

 the Germans " sea-roses," and in this country and in Eng- 

 land " sea-anemones." They are of cylindrical form, bear 

 a circle of tentacles around the mouth at the upper end, 

 and have a muscular base by which they attach themselves. 

 They vary in diameter from one-sixth of an inch to two 

 feet. Some species live in the sand, out of which they get 

 some organic food, and at least one species (Minyas s ) is 

 free-swim m ing. 



Our commonest Northern sea-anemone is Metridium 

 marginatum (Fig. 202), which occurs on rocky shores south 



bladder. 2 o-Kixpos, cup ; fwoz>, animal. 



3 For a figure of Mnyas, see Parker and Haswell, "Text-book of 

 Zoology," p. 189, Fig. 13U. 



