. Comparative anatomy and physiology. Chap IV.] PARASITIC HABITS. 177 The influence of the parasitic mode of life on the organs of digestion is exceedingly well marked. One of the most obvious and common results is the loss by endoparasites of a mouth ; this, among the Protozoa, obtains in the Gregarines, which, living in organs or cavities of other animals (such as the intes- tine of the lobster, or the testicular reservoirs of the earthworm) that are rich in nutrient fluids, obtain their necessary nourishment through their cuticle by the merely physical process of osmosis. Among the ciliated
. Comparative anatomy and physiology. Chap IV.] PARASITIC HABITS. 177 The influence of the parasitic mode of life on the organs of digestion is exceedingly well marked. One of the most obvious and common results is the loss by endoparasites of a mouth ; this, among the Protozoa, obtains in the Gregarines, which, living in organs or cavities of other animals (such as the intes- tine of the lobster, or the testicular reservoirs of the earthworm) that are rich in nutrient fluids, obtain their necessary nourishment through their cuticle by the merely physical process of osmosis. Among the ciliated Infusorians, Opalina is mouthless. The same phenomenon is seen among the Metazoa in Echinorhynchus and the Cestoda, which in their adult condition live always in the di- gestive cavity of Vertebrates. What is certainly true of Tsenia serrata (Fredericq), namely, that no digestive ferment is to be found in any part of its body, is doubt- Fig. 79.—Acineta tube- -, i * ,1 ' f-^ -I rosa with the pseu- JeSS true also OI Other Lestoda, dopoHa extended and and is to be explained by the retracted. fact that these animals live in the midst of food which is being made ready to pass through animal membranes. In another large set of cases food is obtained by suction; among the Protozoa this is seen in the ecto- parasitic Acinetse (Fig. 79), where elongated tubular processes of protoplasm arise from the surface of the body; these tentacles, as they are often called, are capable of very rapid protrusion ; their knobbed ends widen into sucking discs, and are able to pene- trate the cuticle of their prey, which are ordinarily ciliated Infusoria ; the semifluid endosarc is then drawn up through the granular axis of the sucking tube. M—16. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bell, F. J. (Francis Jeffrey), 185
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