HYDROZOA 



131 



tubularian hydroids. These animals are pink in color and move 

 through the water with a graceful swaying motion. 



GENUS Physalia 



P. arethusa, the Portuguese man-of-war. This colony is perhaps the 

 best-known one of the group, since it attracts much attention in Southern 

 waters, and is also one of the most remarkable examples of an animal 

 community. The most prominent part 

 of the compound body is the float, an 

 oblong pear-shaped bag, full of air, which 

 floats on the surface of the water. Its 

 color is bright blue, varying to rose. On 

 the upper side of this air-vessel is a crest, or 

 sail, and from the under side depend long 

 tentacles, or streamers. Some of these ten- 

 tacles are covered with stinging- or lasso- 

 cells ; some are the feeding zooids, with flask- 

 shaped bodies, and some, which look like 

 bunches of grapes, are the reproductive 

 zooids. The tentacles in this curious cluster 

 are all close together and hang from one 

 side of the float, near the broader end. The 

 longest are on the outside, which may be 

 called the windward side, since they serve to 

 keep the crest, or sail, before the wind ; and 

 when the wind is strong they stretch out to 

 a remarkable length, forty to fifty feet, 

 acting as anchors to keep the colony from 

 being driven ashore. They also change its 

 course by raising the pointed end of the 

 float, thus forcing it to " come about." These 

 long tentacles, ordinarily carried more or less 

 curled up, are in bunches of two to four, and 

 emerge from a common stem. Clusters of 

 similar, but smaller, tentacles alternate with 

 the larger ones, but grow somewhat nearer 

 the pointed end of the float ; these are purely 

 locomotive organs. Next come two smaller 

 sets of appendages, also of unequal size, 

 which are the nutritive organs of the com- 

 munity. They are clustered together on a 



Stem like the Others. The appendages Of Pkysalia arethusa. Portuguese man- 



the third kind are small, resemble bunches of ' war ' one flfth natural size - 

 of grapes, and are scattered among the nutritive hydrae. These last 

 are the reproductive zooids of the community. 



GENUS Vellela 



V. limbosa. This hydroid is abundant on the Florida coast. It has 

 a bright-blue, flattened, oblong, bladder-like float, four to five inches 



