. Animal studies. 64 ANIMAL STUDIES their internal organization, so closely resembling that of the free-living forms as to need no further description, in- dicates that they are descendants of the lat- ter. In the greater number the body is flat, and a few species still retain their outer coat of cilia ; but since these are no longer of service as locomotor organs they have gen- erally disappeared, and in their place numer- ous adhesive organs, such as spines, hooks, and suckers (Fig. 35), have arisen, which en- able the animals to hold on with great te- nacity. Thus attached to its host, and
. Animal studies. 64 ANIMAL STUDIES their internal organization, so closely resembling that of the free-living forms as to need no further description, in- dicates that they are descendants of the lat- ter. In the greater number the body is flat, and a few species still retain their outer coat of cilia ; but since these are no longer of service as locomotor organs they have gen- erally disappeared, and in their place numer- ous adhesive organs, such as spines, hooks, and suckers (Fig. 35), have arisen, which en- able the animals to hold on with great te- nacity. Thus attached to its host, and using it as a convenient and comparatively safe means of locomotion, the parasite may still continue to capture, small animals for food or may derive its nourishment from the tissues of the host. In addition there are numbers of internal parasites, living almost ex- clusively in the bodies of vertebrate animals, scarcely a sin- gle one escaping their ravages. 58. Life history.—In the external parasites the young hatch out and with comparative ease make their way to another host; but the young of an internal parasite, inhab- iting the alimentary canal, have a very slight chance in- deed of ever reaching a similar location in another Fig. 35. — A parasitic flatworm (Epidella). m mouth ; o, opening of reproductive system ; s, sucker and spines for attachment. The di- gestive system is stippled ; nervous system black. Enlarged 8 times, from 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 Jordan, David Starr, 1851-1931; Kellogg, Vernon L. [from old catalog].
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Keywords: ., bookauthorjordanda, bookcentury1900, bookdecade1900, bookyear1903
