158 GENERAL BIOLOGY 



attached to the glass, or to the surface film of the water, 

 as well as to the stems; their bodies extended up or down 

 or sidewise; their tentacles extended radially around the 

 mouth. If fully extended, the tips of the tentacles hang 

 vertically in the water and are excessively slender. These 

 are hydra's fishing lines, set for passing water fleas, minute 

 worms, etc., which they paralyze by contact; contracted, 

 they are its arms, and are used for pushing the paralyzed 

 prey into its mouth. Feeding is so slow a process, however, 

 that if one be so fortunate as to see the prey captured he is 

 likely to have to watch some time to see it swallowed. 

 Often the body is seen to be roundly distended in places by 

 previously ingested food in proce'ss of digestion. 



The hydra moves from place to place by turning end over 

 end. It bends over in the desired direction, rests its tenta- 

 cles on its support, lifts its foot and swings it over forward, 

 attaches it and rises again. If the hydra be seen standing 

 on its tentacles with its foot in the air, it is in the midst of 

 one of these turns, wdiich are made, not like hand springs, 

 but with very great slowness. By this means it migrates 

 to the lighted side of the jar. It also moves, but more 

 slowly, by alternate contractions and expansions of its foot : 

 a sort of creeping progression. 



When a number of hydras are present in an aquarium, 

 some of them are likely to show buds growing out from the 

 side of the body. If several well grown buds be present on a 

 single individual they make it appear somewhat more 

 "hydra headed," since on the divided body there are then, 

 if not heads, at least divergent tentacled tips. The buds, 

 however, separate before they attain the full size of the 

 parent. Their development may be traced in stages found 

 in different individuals. First, there is an outpushing of the 

 body wall in a little rounded knob; this elongates into 

 tubular form ; there it develops a whorl of tentacles that 



