Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 174 COMPARATIVE ANATOMY. appear to be excretory products. In the Trematoda these con- cretions are collected into the large trunks, which contract and drive them into the terminal vesicle, whence they are evacuated by the porus excretorius. An anastomosis of the finest ramifications of the canals may be often made out in the Cestoda, as well as in the Trematoda (Distoma dimorphum), and may even affect the larger vessels, which either become connected in a simple manner (into a ring in Dist
Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 174 COMPARATIVE ANATOMY. appear to be excretory products. In the Trematoda these con- cretions are collected into the large trunks, which contract and drive them into the terminal vesicle, whence they are evacuated by the porus excretorius. An anastomosis of the finest ramifications of the canals may be often made out in the Cestoda, as well as in the Trematoda (Distoma dimorphum), and may even affect the larger vessels, which either become connected in a simple manner (into a ring in Distoma rhachiasum, and into regularly succeeding transverse canals in many Cestoda) ; or become converted into a rich rneshwork, in which the chief trunks disappear. The excretory organs in the Nematkelminthes, which again may be derived from a caecal tube, are simpler in character. They form tubes or canals, which pass along the body embedded in the lateral arete (Fig. 61, A r). Near the fore-gut the canals of either side bend towards one another, and unite into a common portion of varying length, which opens to the exterior by a pore in the ventral line. Sometimes these canals are coiled, and they vary greatly in the way in which they are connected with the pore. In the Gordiacea this apparatus appears to be rudimen- tary, for in Mermis it is simply repre- sented by a row of cells, and Gordius, in which there are no lateral tracts, has no distinct organ of this kind. It is doubtful whether the organs found in the anterior region of the body in the Acanthocephali, which are known as ' lemnisci/' belong to the excretory system or not. They form two longish lamellae, without a lumen, which are processes of the body-wall, and like it are provided with branches of canals, between which dark granular masses occur. § 143. When a ccelom is formed, the cha- racters of the excretory organs are so far altered that the canals communi- cate with it by internal ciliated orifices. This new co
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