INSECT'S STOMACH SNODGRASS 371 



products were probably absorbed into the body cavity and there 

 distributed to the other cells tliat had given up the power of individ- 

 ual digestion. Life must have been indeed sublime in those days 

 before stomachs, when one could literally wallow in his food or even 

 sleep in it — unless something disturbing happened in the environment. 

 Unfortunately, however, something is always likely to ha}>pen to an 

 animal in repose, and none of us likes to be disturbed during meals. 



The ancestral blastula, pressed by the necessity of removing the 

 hazards to its digestive composure, hit upon the simple expedient of 

 withdrawing its digestive surface into the interior of the body. 

 Here, in a sheltered food pocket (fig. 4 C, Gc.),, digestion could 

 leisurely go on, and there would be no danger of loss of food to a 

 stronger competitor or by adverse currents of water, for the creature 

 could simply swim away with its food inside it. By this evolution- 

 ary act, which was an anatomical involution but amounted almost to 

 a physiological revolution, the blastula invented the -first stomach. 

 The organ was found to be so successful that it has come to be a 

 standard part of the equipment of all the metazoic animals. Be- 

 cause of its great antiquity, and because of its historic importance, 

 embryologists have commemorated this primitive stomach by giving 

 it the fitting title of archenteron {i.e., most ancient intestine). Fur- 

 thermore, by this same act of establishing an internal stomach, the 

 blastula, in terms of embrj^ology, changed itself into a gastrula, and 

 differentiated its single cell layer into an outer ectoderm. (C, Ecd.)^ 

 and an inner endodcrm {End.). It now became necessary to take 

 food into the stomacli, and thus true eating began. The hole where 

 the stomach was drawn in (C, Bpr.) became the first mouth, though 

 it is called the hlastopore, and served also for ejecting refuse. The 

 stomach cavity is known as the gastrocoele {Gc). 



The establishment of the stomach Avas a great event in the history 

 of us metazoans; nothing quite so important has happened since. 

 Little thought was given then to the sufferings we should later 

 endure in trying to keep the organ decently filled, or the evils that 

 would come upon us from having it overfilled or improperly filled. 



When it is understood now that the word " gastrula " is the 

 diminutive of the Greek gaster., meaning " a stomach ", it is evident 

 that the word gastrulation may be applied to any process of stomach 

 formation. The particular method above described is gastrulation 

 by inv agination.! and most zoologists i-egai-d iuvaginatiim as the 

 probable historic way of stomach formation. Knibryos and other 

 young stages of animals, however, and we shall see more evidence 

 of it, have a vexing habit of distorting history for their own con- 

 venience, Avhen they are expected to repeat it. Embryologically, 

 therefore, gastrulation may take place in other ways than by 



72774—35 25 



