Genus Dero

Identifier: introductiontozo00dave Title: Introduction to zoology; a guide to the study of animals, for the use of secondary schools; Year: 1900 (1900s) Authors: Davenport, Charles Benedict, 1866-1944 Davenport, Gertrude Anna Crotty, 1866- Subjects: Zoology Publisher: New York, Macmillan company London, Macmillian and co., ltd. Contributing Library: MBLWHOI Library Digitizing Sponsor: MBLWHOI Library

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Text Appearing Before Image: ngs is appropriatelynamed Oligocliceta. The aquatic Oligochaeta2 are among the commonestinhabitants of ponds and ditches, living sometimes in themud and sometimes at the surface of the water. Tubifex3 is common in slow-running brooks, and livesin the mud of the bottom, forming tubes in it. Thethread-like bodies of the worm are stretched up beyondthe surface of the mud and wave in the water in gracefulundulations. Often the worms are so numerous that theirreddish color gives a decided tinge to the bottom. Theythrive well in fresh-water aquaria. 1 Annulus, a little ring. 2 A key for the determination of the principal families of aquatic Oligo-chseta is given in the Appendix to this Chapter, page 144. 3 tubus, tube ; face re, to make. THE EARTHWORM AND ITS ALLIED 137 Dero1 is very common on the surface of ponds, particu-larly in the midst of duck-weed (Lemna), the leaves ofwhich it cements together to form a floating tube in whichit lives, and by which it is accompanied in all its migra-

Text Appearing After Image: Fm. 12o. — Dero, the duck-weed worm. Enlarged. After Reighard. Thelettering is as follows: or., mouth ; phx., pharynx ; oe., oesophagus; ftff. .,segmental organ; in., intestine; pav., pavilion or tunnel; dg. app., finger-like appendages. From Reighard. tions. Dero can also be told by the sort of funnel at thehinder end of the transparent body, from the margins ofwhich finger-like filaments arise which aid in respiration(Fig. 123). Nais2 does not construct tubes, and it has no respiratory , to skin (= flay). 2 PCUS, a water-nymph. 138 ZOOLOGY filament at the hinder end of the body (Fig. 124). It also has eyes; while Dero has none. Both Dero and Nais have the interesting habitof reproducing bydividing the bodytransversely. In themiddle of the bodytentacles begin toarise, a new mouth isformed, and the wormconstricts into two.I n d e e d, sometimesseveral new heads maybe forming in themidst of a singleworm. This habit isof advantage not onlyin multiplying thenumber of individual

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