Page:Jardine Naturalist's library Entomology.djvu/153

Rh into the canal in front of the chylifying portion of it. In support of the older and more generally received opinion, that the function of these vessels is analogous to that of the liver, it is alleged, that by their insertion in the intestinal canal they correspond to the gall-secreting organs of other animals; that there is often a bladder-shaped distention where they join the canal, forming a kind of gall-bladder; that the vena porta which conducts the blood to the liver takes its rise from the fatty matter within the ventral cavity, as is the case with the vessels in question; and that the liver of closely allied animals (such as crabs, and annelides) consists likewise of such vascular appendages to the intestine. Amid these conflicting sentiments, a mixed opinion best harmonises with the facts, and such has accordingly been adopted by Meckel, Tiedemann, J. Müller, and Burmeister; viz. that the vessels in question have a double function, sometimes secreting bile, at other times urine. Whether they secrete the one or the other probably depends on the point of their opening into the canal being within the region of the chylific ventricle, or posterior to it. In these circumstances, the name suggested by M. Audouin might be advantageously substituted for the present, for the most accurate knowledge we now possess of the functions of these vessels thus proves them to be urino-biliary. The changes which the alimentary substances undergo in the part of the canal behind the insertion of the vessels just spoken of, depends in some