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-Hving 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 vv^orms 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 ma3^y larva. Further changes are not known 

 except that in the body cavity of various adult insects, such as 



Fig. 832. Enibroyo of Paragordius 

 varius with extended proboscis, X looo. 

 (After Montgomery.) 



