Miscellaneous. d'Vd 



On the Functions of the Glands of the Digestive Apparatus 

 of Insects. By M. Jotjssex, 



The physiological functions of the glands of the digestive appara- 

 tus of insects have not yet been determined with sufficient certainty ; 

 hence the differences of opinion that exist in science as to the part 

 to he attributed to each of these glands in the digestion of food. 



The naturalists who have paid attention to this subject have 

 almost always made use in their researches of the liquid contents of 

 the digestive tube ; and I have thought that the different results at 

 which they have arrived w^ere to be ascribed to this very defective 

 practice, since these liquids are complex and mixed in always 

 unknown proportions, I have therefore sought amongst the various 

 insects for one in which the arrangement of the glandular organs 

 might enable me to collect these liquids in the gland itself, before 

 their entrance into the digestive tube. 



The cockroach {Blatta orientalis) is in this case. The three 

 glandular groups of its digestive apparatus are very favourable to 

 experiment and arranged as follows : the upper region, consisting 

 of an oesophagus, a crop, and a trituratory apparatus, bears oesopha- 

 geal glands in bunches, called salivar)) glands, nearly 1 centim. in 

 length ; the middle region or stomach presents eight glandular 

 ca3ca, 4 or 5 millims. in length ; and, lastly, the lower region, or 

 intestine, bears Malpighian tubes which are easily isolated. These 

 three glandular apparatus occur in all insects ; but they vary much 

 in dimensions, and are usually too small to enable us to collect the 

 contents in a state of purity. The cockroach thus forms a fortunate 

 exception. 



By experimenting with these liquids collected before their 

 entrance into the digestive tube, I have been able to ascertain that 

 the sole agent in the digestion of amylaceous matters is the se(5re- 

 tion-product of the oesophageal or salivary glands. I have con- 

 vinced myself, by direct experiment, that none of the other glands 

 possesses a marked action upon amjdaceous substances, and that the 

 secretion-product of the salivary glands has no action upon the 

 alburaenoid and fatty foods. I think that the digestion of feculent 

 substances takes place principally in the crop in those insects which 

 have the oesophageal glands greatly developed, like the cockroach — ' 

 and that when these glands are small and lodged in the walls of 

 the oesophagus, this digestion, which in this case is of little impor- 

 tance, takes place in the stomach. The glucose produced is absorbed 

 by the stomach and does not pass into the intestine. 



The caeca which surround the stomach are endowed with quite 

 different properties. They secrete a yellowish liquid, which is feebly 

 but distinctly acid. After collecting a sufficient quantity, I ascer- 

 tained that, as already stated, it has no action upon amylaceous 

 matters, but that it dissolves with remarkable energy the albumenoid 

 substances, coagulated albumen, caseine, and in particular fibrine, 

 of which it rapidly liquefies as much as twice its own volume. I 



