SOME UNSOLVED SCIENTIFIC PROBLEMS 



plicated, but the accumulating researches are just at a 

 point where much is obscure about many of the ob- 

 served phenomena. The immediate future seems full 

 of promise of advances upon present understanding of 

 cell processes. But for the moment it remains for us, 

 as for preceding generations, about the most incom- 

 prehensible, scientifically speaking, of observed phe- 

 nomena, that a single microscopic egg cell should con- 

 tain within its substance all the potentialities of a 

 highly differentiated adult being. The fact that it 

 does contain such potentialities is the most familiar of 

 every-day biological observations, but not even a 

 proximal explanation of the fact is as yet attainable. 



- 



The Ancestry of the Mammals 



Turning from the cell as an individual to the mature 

 organism which the cell composes when aggregated 

 with its fellows, one finds the usual complement of 

 open questions, of greater or less significance, focaliz- 

 ing the attention of working biologists. Thus the 

 evolutionist, secure as is his general position, is yet in 

 doubt when it comes to tracing the exact lineage of 

 various forms. He does not know, for example, ex- 

 actly which order of invertebrates contains the type 

 from which vertebrates sprang, though several hotly 

 contested opinions, each exclusive of the rest, are in 

 the field. Again, there is like uncertainty and differ- 

 ence of opinion as to just which order of lower verte- 

 brates formed the direct ancestry of the mammals. 

 Among the mammals themselves there are several 

 orders, such as the whales, the elephants, and even 

 man himself, whose exact lines of more immediate an- 



227 



