CHAPTER XI 



THREADWORMS, HAIRWORMS, AND BRISTLE- 

 WORMS 



Nematoda and Oligochaeta 



Similarity of worms and midge larvae. — All are not worms 

 which wriggle; nowhere is this more true than in the mucky- 

 trash of pond shallows and the weed-grown side-waters of 

 streams where thousands of insect larvae, almost all of them 

 midges (p. 291), abound in close company with true thread- 

 worms or nematodes and bristleworms or oligochaetes.' All 

 of these are about the same length, mostly under a quarter of 

 an inch; to the naked eye they look alike, but if they are 

 examined with a hand-lens their differences will at once appear 

 (Fig. 109). The midge larvse have distinct heads, segmented 

 and almost hairless bodies, usually two fleshy prolegs near the 

 head and two at the rear; such prolegs occur along the abdo- 

 men of any common caterpillar. These are never found upon 

 worms. The nematodes are as slender as "midge larvae but 

 they have no heads, their bodies are unsegmented and without 

 an appendage of any kind. Most fresh water oligochaetes 

 are either little transparent bristly worms or small aquatic 

 earthworms easily recognized as such. They have no heads 

 and their bodies are divided into segments bearing homy 

 bristles that are used as feet. The midge larvae along with 

 the nematodes and the smaller oligochaete worms constitute 

 a great host of minute animals which are constantly devouring 

 plant tissues, especially soft ones, continually cleaning up 



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