374 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1925 



farther and farther removed from the understanding of the gtneral 

 readier. This state of affairs is to be deplored, because one of the 

 purposes of science, at least of scientific institutions that employ 

 scientists, is the diffusion of knowledge, and knowledge is not dif- 

 fused by writings in wliich the secrets of nature seem to b? just as 

 carefully guarded from the public understanding as they are in the 

 various realms of nature herself. 



Another thing that contributes to the unreadableness of much 

 scientific writing is the laudable desire of the scientist to give full 

 credit where credit is due; but this often overloads his text v/ith 

 citations of references and authorities, and so breaks up the con- 

 tinuity of his account that the general reader soon tires in an attempt 

 to follow it. What then shall we do? The only solution seems to 

 be that for scientists we must write as scientists, for the general 

 reader we must clear away all but the essentials, though letting it 

 be known that we do not pretend to first-hand knowledge of more 

 than a small percentage, if any, of the facts related. 



In the following pages an attempt will be made to tell, with a 

 minimum of technical terms, the story of the development of an 

 insect from the germ cells to the creature at hatching. The facts 

 of development and heredity, however, are exceptionally difficult to 

 put into ordinary words, for the reason that they constitute phases of 

 growth that are in many ways quite different from those with which 

 we are more familiar. And yet, for descriptive purposes, things must 

 have names. Therefore, where only a scientific name is available, 

 that name must be used, and if the writer makes all possible conces- 

 sions to a popular vocabulary, the reader, on his part, must agree 

 to learn a few indispensable terms of technical embryology. 



THE GERM CELLS 



The materials of which living matter is composed consist mostly 

 of substances that the chemists call unstable — which is to say, they 

 are complex compounds that naturally break down into their simpler 

 and more stable components. For this reason the physical substance 

 of life must be continually renewed. All animals and most plants 

 have a limited space of time during which they are able to repair 

 their waste and remain alive. A large proportion of them, too, never 

 attain their possible old-age limit, falling victims at an earlier age 

 to other devouring animals, to parasites, and to diseases. Hence, 

 even though each individual were capable of living forever, its chance 

 of doing so would be slim ; sooner or later it would almost certainly 

 be destroyed in one way or another. To insure continuity of life, 



