464 



RADIATA: ACALEPH^E. 



FIG. 699. 



nals of different kinds, yet all 

 so combined as to give the ap- 

 pearance of one animal. The 

 " Portuguese Man-of-War," of 

 the Gulf of Mexico, is of this 

 sort. It consists of an elegantly 



crested air-sac, 



floating 



upon 



the water, and giving off nu- 

 merous long and varied append- 

 ages. According to Agassiz, 

 these are the different members 

 of the community, and fulfill 

 different offices ; some of them 

 eating for the whole, others pro- 

 ducing medusa buds, and others 

 being the locomotive or swim- 

 ming members, and having ten- 

 tacles that stretch out behind 

 the floating community to the 

 length of twenty or thirty feet. 

 According to Agassiz, there 

 are some kinds of Acalephs 

 which produce coral similar to 

 that formed by Polyps, described 

 in the following pages. Mille- 

 porcb is a genus of coral of this 



sort (Fig. TOO.) 



To the Hydroidea belong also the so-called " fresh-water 

 polyps" (Hydra). These are common in fresh-water 

 ponds and streams, and are found attached to the stems 

 and leaves of aquatic plants. They are merely a living 

 tube-like sack, with the margin prolonged into eight ten- 

 tacles. They have become celebrated on account of the 



Portuguese Man-of-War, Physalia 

 aretkusa. 



