Miscellaneoua. 395 



MISCELLANEOUS. 



Oti the Histology of the Alimentary Canal in the Larva of 

 Chironomus plumosus. By P. Vignon. 



I. Criticism on the Vesicular Theory of the Secretion of Glandular 

 Merocrine Cells. — I thus characterize the theory held with regard 

 to renal cells by a long list of authors, from Muron in 1871 down 

 to Simon in 1898 (also by Coruil in 1879 and 1884, Altmann, 

 Nicolas, Van der Stricht, Disse, &c.), and criticized by Hortoles 

 in 1881 and by Sauer in 1895. This theory was applied by Van 

 Gehuchten in 1890 to the intestine of a dipterous larva, Ptycho- 

 ptera ; then in 1893 to the intestine of the larvae of the fly, of 

 Ascaris, and of Arenicola^ «S:c. It is accepted by most authorities, 

 and I know of no criticism of it so far as it relates to intestinal 

 cells *. 



The tissues of the larva of Chironomus being quite transparent, 

 observations made upon the fry, and even on the complete animal 

 when very young, point to the following conclnsions : — the hyaline 

 vesicles which support the brush-like edge (or striated platform — 

 " plateau ") seen on the greater part of the cells of the mid-gut, and 

 which afterwards show it up and spread into the caeca or the 

 chylific stomach, as well as into the Malpighian tubules, without 

 anywhere being dissolved, are the result of a pathological state or 

 of some very light pressure, or, again, of the action of a fluid said 

 to be indifferent, and with more likelihood of fixative solutions. 



Not a single one is ever seen in the living and uninjured animal 

 even when digestion is in full swing. One has no right to draw con- 

 clusions from these plasmolytic changes as to the secretory properties 

 of the epithelial cell ; they are simply a proof of the great ease with 

 which it may undergo alteration. 



I shall endeavour to ascertain eventually whether these con- 

 clusions apply to all the glandular merocrine cells. 



II. Formation of the Peritrophic Membrane. — This chitinous 

 membrane, imperforate but at the same time extremely permeable, 

 has no connexion with the walls of the chylific stomach, at least in 

 the present case. This is in direct opposition to the somewhat 

 indecisive opinion of Plateau in 1876, of Balbiani in 1890, and to 

 the plainer statement of Voinov in 1898. The last observer believes 

 it to be formed of all the cell-plates supported by the secretive 

 vesicles. Although it may be firmly fixed to the external wall of 

 the oesophageal tube, as has been observed by A. Schneider in 1887, 

 followed by Balbiani in 1890 (in both cases in the larva of Chh'o- 

 nomus), it is not formed in that position. It arises in a fluid state 



* I may refer to the statement which I made in vol. iii. of the ' Ann^e 

 biologique ' in the course of a review entitled " Les Canalicules urinaires 

 des "\'ert6br^s.'' 



