334 Miscellaneous. 



have also ascertained that the albumenoids were not simply dissolved, 

 but transformed into true peptones, no longer coagulable by heat or 

 by acids, but only by bichloride of mercury. 



The liquid of the caeca further possesses the property of energeti- 

 cally emulsionizing fats, a property which is not shared either by 

 the salivarj' glands or by the Malpighian tubes. This emulsion 

 lasts for a very long time and acquires a marked acidity. 



We see, therefore, that in a general way the product of the gastric 

 caeca constitutes the most important agent of digestion in insects ; 

 and those of them which, like the herbivorous insects, feed upon 

 substances difficult of digestion, possess innumerable gastric caeca 

 and have at their service a great quantity of this liquid. This pro- 

 perty of emulsionizing and acidifying fatty matters, which the 

 gastric juice of the Yertebrata does not possess, appears to approxi- 

 mate this product of secretion to the pancreatic juice ; and the 

 assimilation would be complete if it applied also to the amylaceous 

 substances ; but we have seen that this function belongs exclusively 

 to the oesophageal glands in the digestion of insects. Nevertheless, 

 taking into consideration the weak acidity of the liquid of the caeca 

 and its action upon fats, I incline to regard it as presenting much 

 analogy with the pancreatic juice, the character of the action upon 

 starches not being primordial in the pancreas, as M. Claude Bernard 

 has demonstrated that, in certain fishes, this organ is already 

 destitute of action upon amylaceous matters. 



However this may be, I believe that the peptones formed in the 

 stomach and the fatty emulsions are absorbed at once by the walls 

 of the stomach, which is the essential part of the digestive apparatus 

 and plays the double part of the stomach and the small intestines of 

 the Vertebrata. The materials which have resisted these actions, 

 and which are consequently unfit for digestion, alone pass into the 

 intestine, which I regard, as playing scarcely any part in digestion 

 properly so called. 



The Malpighian tubes in these researches have always offered 

 clearly negative characters. Their product of secretion does not act 

 upon amylaceous substances, or upon albumenoids, or upon fatty 

 matters. This confirms the opinion generally adopted that this 

 group of glands is purely and simply an organ of excretion, a 

 urinary organ probably more complete than that of the Yertebrata, 

 since it is the sole eliminating organ of insects. The presence here 

 of uric acid and of urates has long since been ascertained ; but 

 perhaps they furnish other principles analogous to the excrementitial 

 matters that the liver has to eliminate in the Yertebrata. 



These researches confirm the opinion long ago maintained by M. 

 Blanchard as to the very high grade that insects should occupy in 

 the animal series. We see, in fact, that their digestive functions 

 greatly approximate to those of the higher Vertebrata. — Comptes 

 Bendus, January 3, 1876, p. 96. 



