THE CONTROL OF LIFE 103 



Siamese twins in sea urchins by causing 

 the egg to extrude a part of its contents 

 and so that there were two portions imi- 

 ted by a bridge of protoplasm. In many 

 cases each portion developed, forming 

 two individuals connected by a ligature. 

 In the same way triplets could be pro- 

 duced. 



It would seem needless to multiply 

 instances, for these few examples suffice 

 to show that the experimenter has power 

 to control development to a remarkable 

 degree. We may, however, inquire to 

 what extent the modifications produced 

 by the experimenter are hereditary. 



It is often stated that simple one-celled 

 organisms, such as bacteria, can be mod- 

 ified by treatment so that they and 

 their descendants are noticeably altered. 

 Thus it is a common practice to decrease 

 the virulence of bacteria so that they 

 may be used for various purposes. We 

 must bear in mind, however, that the 

 culture may contain different strains and 

 that the treatment may do nothing more 



