JUGGLING WITH LIFE 



more curious, undertaking to bring about the substi- 

 tution of one organ for another. He applied his test 

 to certain marine forms known as hydroids and 

 ascidians with entire success. 



There is, for example, a hydroid that is called a 

 tubularian because its body consists of a long tube, 

 one end of which is attached to the sea bed by a 

 stolon or foot, while the other end, representing the 

 head, is a fringe-like mass of tentacles with a mouth 

 for the ingestion of food. Professor Loeb cut off 

 both ends, and inverted the tube so that the end from 

 which the head would normally grow was fixed in 

 the sand, the foot end being free in the water. Under 

 these circumstances a new head forms where the foot 

 had normally been. It is even possible, in some 

 cases, to develop a head at each end of the stem. 



This process of so-called heteromorphosis is illus- 

 trated in a striking way, as Professor Herbst has 

 shown, in the case of a creature much higher in the 

 organic scale, namely, a crustacean, allied to the 

 familiar crab. Here if an eye is removed, the sev- 

 ered organ may be replaced by an antenna. Indeed 

 this is sure to take place if the optic ganglion is re- 

 moved. On the other hand if this ganglion is left 

 intact, a new eye is formed apparently quite as good 

 as the old one. 



RESTORING LOST MEMBERS 



The growing of a new eye of this highly specialized, 

 type is a striking phenomenon. But it must be re- 

 called that the crab and its allies have remarkable 

 properties of regenerating lost members. It has long 

 11 153 



