ABSORPTION OF SOLUBLE PRODUCTS OF DIGESTION 329 



undergo special modifications, and are transformed into solid prod- 

 ucts, which are situated at the bottom of these cells. Afterwards 

 the alimentary substances freed from a portion of their useful sub- 

 stances are again placed in contact with the products of secretion in 

 the distal part of the chylific ventricle, and reach the terminal part 

 of the intestine. 



" The products of secretion," adds Gehuchten, " diverted into the 

 intestinal canal do not come into immediate contact with the alimen- 

 tary substances ; they are separated from it by a continuous, struct- 

 ureless, quite thick membrane (the peritrophic membrane), which 

 directly envelops the cylinder of food matters, extending from the 

 orifice of the oesophageal valvule to the end of the intestine. 

 Between this membrane and the free face of the epithelial lining 

 there exists a circular space, into which are thrown and accumulate 

 the excreted substances. The latter then cannot directly mingle 

 with the aliments ; but when they are liquid they undoubtedly pass 

 through this membrane by osmose, and thus come into contact with 

 the nutritive substances. It is the same with the products of 

 absorption. The absorption of soluble products of the intestinal 

 cavity is not then so simple a phenomenon as it was at first thought 

 to be, since these products are nowhere brought into immediate con- 

 tact with the absorbent cells" (pp. 90, 91). 



The most recent authority, Cuenot, states that absorption of the 

 products of digestion takes place entirely in the mid-intestine, and 

 in its caeca when these are present. The mid-intestine exercises a 

 selective action on the constituents of the food comparable to the 

 action of the vertebrate liver. 



LITERATURE ON THE PHYSIOLOGY OF DIGESTION 



Davy, J. Note on the excrements of certain insects, and on the urinary excre- 

 ment of insects. (Edinburgh New Phil. Journ., 1846, xl, pp. 231-234, 



335-340 ; 1848, xlv, pp. 17-29.) 



Some observations on the excrements of insects, in a letter addressed to 



W. Spence. (Trans. Ent. Soc. London, Ser. 2, iii, 1854. pp. 18-32.) 

 Bouchardat. A. De la digestion chez le ver a soie. (Revne et Mag. de Zool. , 



Se"r. 2, 1851, iii, pp. 34-40.) 

 Lacaze-Duthiers, H., et A. Riche. Me"moire sur 1'alimentation de quelques 



insects gallicoles et sur la production de la graisse. (Ann. Scienc. natur., 



1854, Se"r. 4, ii, pp. 81-105.) 

 Basch, S. Untersuchungen tiber das chylopoetische und uropoetische System 



von Blatta orientalis. (Sitzungsber. d. math.-naturwiss. Classe d. Akad. 



d. Wissensch. Wien., 1858, xxxiii, pp. 234-200, 5 Taf.) 

 Lambrecht, A. Der Verdauungsprozess der stickstoffreichen Nahrmittel, welche 



unsere Bienen geniessen, in den dazu geschaffenen Organen derselben. 



(Bienenwirtschaftl. Centralbl., viii Jahrg., 1872, pp. 73-78, 83-89.) 



