HYDRA FUSCA 147. 



X 



and then, by the contraction of the body wall, forced downward 

 to the basal end of the cavity. Here it is mixed with the diges- 

 tive juices of the animals and slowly digested. In time the diges- 

 tive parts are dissolved and absorbed into the cells that form 

 the body wall and are assimilated. After all the nutritious por- 

 tions have been digested and absorbed from the food particles, 

 the undigested refuse is then ejected from the mouth by a sudden 

 contraction of the body and opening of the mouth, which throws 

 the ejected portions some distance from the animal. As the 

 result of digestion and assimilation, the animal grows. 



After it reaches a certain size, rarely more than one-half an 

 inch in length, the further growth shows itself in the formation 

 of buds which appear on the sides of the old individual; see 

 Fig. A. These buds rapidly increase in length, and after a 

 time a circle of minute secondary buds can be seen at their tips. 

 These secondary buds are rudimentary tentacles, for they in- 

 crease in length till eventually they become new tentacles. In 

 the middle of the circle of tentacles thus formed a small opening 

 makes its appearance, which forms a new mouth at the end of the 

 growing bud. After a time the bud itself separates from the body 

 of the animal from which it grew and floats off by itself as an 

 independent individual, identical in structure with the one from 

 which it came, though somewhat smaller. In this way the 

 Hydra reproduces itself indefinitely by budding (gemmation) as 

 long as it has sufficient food and proper conditions for feeding 

 and growth. If the conditions are favorable two or more buds 

 may be seen arising from the same individual, and occasionally 

 a secondary bud may be found arising from the side of the bud, 

 even before it has broken away from the animal that produced 

 it. In the case of the Hydra, however, these buds do not remain 

 attached very long, but always separate; so that we never find 

 the animals grouped together in great masses. While we may 

 find one Hydra with one, two, or three buds, this is the extent 

 of group formation. In closely allied animals, however, the 

 budding may go on almost indefinitely, and groups are formed 



