. Fresh-water biology. Freshwater biology. 536 FRESH-WATER BIOLOGY aid of a microscope. The most of the features on which classifi- cation is based are external and must be regarded as arbitrary and trivial. The internal structure can be studied only with difficulty by complicated technic and may be passed here without description. In one respect the Gordiacea differ from the parasitic worms heretofore considered: the adults are free-living and it is only the young stages which carry on a parasitic existence. Probably the free aquatic stage is merely a reproductive period, even though it is pr
. Fresh-water biology. Freshwater biology. 536 FRESH-WATER BIOLOGY aid of a microscope. The most of the features on which classifi- cation is based are external and must be regarded as arbitrary and trivial. The internal structure can be studied only with difficulty by complicated technic and may be passed here without description. In one respect the Gordiacea differ from the parasitic worms heretofore considered: the adults are free-living and it is only the young stages which carry on a parasitic existence. Probably the free aquatic stage is merely a reproductive period, even though it is prolonged for several weeks or months. The worm when loaded with eggs is round and plump, but the spent female is often wrinkled and flattened. Gordius deposits its eggs in a long white or grayish cord which may be several feet long and apparently many times the bulk of the female worm. In some species the cord breaks up into shorter pieces. The virorms are often observed in knotted masses, con- sisting of two or more worms coiled together. In some cases at least they are coiled about the egg strings and remain for many days in this position, thus in a sense exercising protection over the developing embryos. It is commonly said that the Gordiacea de- posit their eggs in brooks or other running water, but I have found some species in abundance on water plants and in knotted masses along the shore of Lake St. Clair, Lake Erie, and Lake Michigan. Rarely I have seen a conspicuous windrow of adult worms and egg masses extending for some distance along the water's margin of an inland lake and probably washed up there by wave action. The minute embryo (Fig. 832) which hatches from these eggs after a brief period possesses a conspicuous proboscis and set of hooks at the anterior end. By this powerful boring apparatus the em- bryo forces its way into some aquatic insect, often the mayfly larva. Further changes are not known except that in the body cavity of various adult insects, such as.
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectfreshwa, bookyear1918
