868 ANNUAL REPOflT SMITHSONIAN INSTITUTION, 193 3 



digestion products must be substances of the kind that can be used 

 in the constructive i^hase of protoplasmic metabolism. The inges- 

 tion of digested food material through the cell wall is generally 

 designated absovption. In the case of the many-celled animals the 

 absorbed food materials, furthermore, must pass clear through the 

 stomach cells (fig. 3 B, c?), or through other cells of the digestive 

 tract, in order to be distributed (e) in the body liquid (blood) to 

 the nondigestive cells of the body. 



The method of feeding by absorption is practiced by most of the 

 body cells of nearly all the many-celled animals, though, of course, 

 all the cells do not do their own digesting — some live in a medium 

 containing food already digested by some other set of cells or by 

 some other organism. Certain animals harbor in their food tracts 

 bacteria or protozoa having the power of digesting certain sub- 

 stances that they themselves cannot handle, and thus may thrive 

 on a diet that would mean certain starvation to any ordinary 

 creature. 



A method of accomplishing some particular function in a certain 

 way having once been adopted and handed down from generation 

 to generation, an organ is almost sure to be evolved in which the 

 function becomes localized. In the case of digestion the organ is 

 the stomach. The stomach is a common inheritance of all the 

 present-day many-celled animals, which is to say, it originated with 

 the early ancestors of these animals and has been transmitted to all 

 the descendants, with, of course, various modifications and improve- 

 ments to suit individual needs. Hence, though our particular sub- 

 ject is the history of the insect stomach, the same history in a gen- 

 eral way applies to all stomachs, including our own. Let us see, 

 then, how stomachs began. 



When an habitually scientific writer starts out to write a " popu- 

 lar " article, the first thing he thinks he must do is to adopt the first 

 person plural; it makes him feel chummy with the reader, and he 

 assumes that the reader will now easily understand all he is writing 

 about. Then he plunges ahead in the most technical kind of lan- 

 guage about things most people never saw or heard of. It is, there- 

 fore, somewhat disconcerting, now that after a long preliminary we 

 have reached a point where the real subject of this story might be 

 introduced, to realize that the history of stomachs is involved in 

 zoological matter that a considerate writer should not assume to be 

 perfectly well known to the reader. Hence, it will be appropriate to 

 explain here a few important things about animals in general, and 

 about certain groups of animals in particular, in order to define some 

 technical words and in order to make certain ideas appear more 

 reasonable than they might otherwise seem. 



