MYSTERIES OF LIFE AND EXISTENCE — SNODGRASS 525 



of the parent species. The geneticists and biochemists tell us that 

 on the chromosomes of the cell nucleus is encoded the entire plan for 

 the development of the embryo, which serves as a working blueprint 

 for the developing cells. To clarify this somewhat anthropomorphic 

 statement, it must be explained that the language of the code is that 

 of molecular chemistry, which the biochemists are industriously trying 

 to interpret. (See numerous papers in the Scientific American dur- 

 ing the past 10 years.) The code characters are said to be different 

 combinations of the component elements of the DNA molecules. The 

 message is delivered in the form of enzymes, but tlie language of 

 enzymes has not been fully translated. 



Though the fact of embryonic development from a single cell is 

 commonplace knowledge, that it is done by the chemically guided 

 interaction of cell molecules is almost unbelievable. Yet no other 

 power can be invoked, no outside force normally affects the embryo. 

 Though the chemical basis of embryogeny may be a mystery beyond 

 our comprehension, we have to accept it as a fact. It makes us one 

 with the physical universe. Without DNA we might still be one-celled 

 animals. 



Wlien the embryo is once established, DNA seems to delegate its 

 authority largel}'- to organizers. An organizer is any part of the em- 

 br3^o that induces a neighboring part to develop in a particular way. 

 The effective chemical substance emitted by an organizer is called an 

 evocator. That chemicals can produce specific forms of growth in 

 living tissue is clearly demonstrated in the formation of plant galls by 

 insects. Something injected into the plant by the female insect when 

 she inserts her eggs, or sometliing excreted by the larvae, causes an 

 abnormal growth of the plant tissue into a gall specific of the insect 

 species that caused it. 



CELL MOVEMENTS 



The free-living Protozoa are one-celled motile animals; in fact it 

 is because of their movements that we recognize them as living things. 

 Simplest of them is the amoeba, a minute shapeless mass of proto- 

 plasm, and yet it moves, ingests particles from the water, digests and 

 assimilates those of food value, ejects the others, reacts to external 

 stimuli, and reproduces itself. The amoeba thus performs all the 

 essential functions of the higher animals, but does them in a very 

 simpler maimer. 



The amoeba moves in an}^ direction by throwing out fingerlike proc- 

 esses of its body called pseudopodia. Since it can project pseudopods 

 from any part of its body, it has no permanent anterior or posterior 

 end. If it comes into contact with a solid object, it turns one way or 

 another, just as would any other living animal. But what is life in 

 such a simple creature? The experimentalists tell us (see Meier and 



