HYDRA 



271 



contains many small species, which are easily cajjtured in the 

 net, and which are of extreme beauty and delicacy. 



Besides the HydromedusEe, the group of Hytlrozoa includes 

 the siphonophores/ These animals are always colonial and 

 free-swimming, and are among the most beautiful inhabitants 

 of the sea. Those who have crossed the Atlantic are ac- 

 quainted with the " Portuguese man-of-war " (Phj-salia,- 

 Fig. 262), which often swarms in the Gulf Stream. The huge 



Fig. 261. 



-A large jellyfish that has no hydroid stage {Zijrjodactjjlo). 

 diiccd. From a drawing by A. Agassiz. 



Re- 



float which lies on the surface of the water serves also as a sail 

 by which the animal is transported bjr the wind. There are 

 other smaller, more graceful species of more tyi^ical form (Fig. 

 262 a). The structure of a siphonophore is veiy 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 (forms which 

 produce the germ-cells). There are leaf-like expansions, also, 

 which are rudimentary jellyfishes. All the man,\' forms budded 

 on the stem are modifications of the hj'droid type. 



Contrasted with the Hydrozoa are the beaker animals 



■ siphon, a siphon ; plwrus, l^earing 



- bladder. 



