. THE ALIMENTARY CANAL AND ITS GLANDS. 101 



The only conclusion, then, that we are really warranted in draw- 

 ing concerning the origin of the royal jelly or of any of the larval 

 food paste is that we do not know anything about it. Cheshire is 

 probably responsible for the widespread opinion that it is formed 

 by the pharyngeal glands, though Schiemenz (1883) published a 

 large paper containing this theory three years before Cheshire's 

 book was printed. The " chyle " theory, which also has many advo- 

 cates, originated with Dufour but was principally elaborated b}' 

 Schonfeld. Arnhart would derive the brood food from both the 

 stomach and the glands. But we are still absolutely in the dark, 

 since we lack definite and conclusive information. A satisfactory 

 study of the subject would involve the chemical investigation of 

 very minute quantities of substances, and it may be a long time before 

 any interested person is found capable of undertaking a work of thi-t: 

 sort. The writer of the present paper is professedly preparing an 

 account only of the structure of the organs, but is doing this with 

 the hope that it may furnish a basis for some future investigator who 

 shall have time to devote himself to a study of the chemistry and 

 physiology of the digestive organs and their glands. 



In vertebrate animals the digestive secretion of the stomach is acid 

 and its enzymes bring abont especially the digestion of proteids. The 

 resulting acid mixture is called cliymc. In the intestine the contents 

 are flooded with various alkaline liquids whose enzymes then take up 

 the digestion of the other food elements. The final prepared product, 

 which is absorbed by the lacteals, is called cltyle. These names have 

 been applied to the contents of the alimentary canal in insects — espe- 

 cially by Arnhart (lOOG), who speaks of the material undergoing 

 digestion as '' chyme "" and the completed products as " chyle." But 

 absolutely nothing is known of the digestive process in insects beyond 

 the fact established by Plateau (187-1) that the contents of all parts of 

 the alimentary tract are alkaline during digestive activity and either 

 neuti-al or weakly alkaline at other times. Hence, if we make use of 

 these words in insect physiology, it must be w^ith the understanding 

 that no chemical significance is implied. The ventriculus is very 

 commonly called the '* chyle stomach " but there is probably no reason 

 for calling it a " chyle stomach " any more than a " chyme stomach," 

 and like^^ ise there is no reason for supposing that the intestine does 

 not contain chyle — in fact, it almost certainly does. The w^ord 

 " chyle " may be used with entire propriety in insect physiology to 

 signify the completed products of digestion, but to designate a part 

 of the alimentary tract as the " chyle stomach " is applying the term 

 without an adequate basis of facts. 



The contents of the ventriculus are surrounded by several concen- 

 tric layers of thin filmy membrane which form an interior tube ex- 

 tending the entire length of the stomach and reaching down into the 



