WORMS. 



223 



type is a very long and slender worm, discovered by Professor Leydig, wliich displays 

 a marked predilet-tioii for deep wells. As far as I am aware it has hitherto been 

 found only in Germany. 2. Tubificid^. Tiie common and graceful lubifex makes 

 an interesting iidiabitant of a small fresh-water aquarium. It is easily obtained by 

 digging uj) some dark mud from the bottom of almost any meadow brook, and then 

 placing it with water in a jar; when the settling is completed the worms will soon 

 reconstruct their long tubes which run down from the surface of the mud; thev will 

 then stretch forth their long slender bodies, which undulate incessantly until some dis- 

 turbance causes the frightened worm to jerk back into its domicile. The annual is long 

 and slender as a thread, somewhat reddish in color and transjiarent. Witii a lens 

 the segments of its body may be readily distinguished, and the little lateral bristles ; 

 those of tiie lower row are forked and hooked : similar bristles, together with simple 

 liair-shaped ones, form the ujiiK^r row. Along the New England coast the allied genus 

 VUtdlio is common, being, unlike Tiibife.c., an inliabitant of the ocean ; it is found, in 



I'lireiiriictes 



company witli two or three other cognate genera, under stones and decaying sea-weeds 

 near high-w'ater mark. 



The members of the third family, KN('nYTiivEn).E, live in the earth, rotten woods, 

 waters of swamps and the ocean. The I'ed-blooded Pachi/drilus may be taken as 

 typical ; it being a common marine genus. The last family, the Naid^s:, coraju-ises 

 the best-known and most interesting members of the order, the two chief genera, Kais 

 and (^luMof/aster, liaving been studied again and .-igain by naturalists during the 1,'ist cen- 

 tury and a half, their wonderful repnidurtioii liy transvcTM' (ii\ InIom always i)ossessing 

 a vivid interest. The Naida^ are small, transparent worms, which may.be readily cap- 

 tured by scooping blindly through tlie plants gi-owing in fresh water, among which 

 these creatures swim about. Many of them have a long snout or horn growing out 

 from tiie head. Very comuujn is the Nais proboscklea, which has a relatively immense 

 a[)[)endage " jiroaking out before its eyes." This long trunk is used to feel the way. 

 Another member of the same genus, howi'\rr, has a simple roundeil lie;id. The genus 

 itself is e.'isilv recourui/.eil bv the fact th;it the upper I'ow of bristles on each side are 

 h.air-likc', wliilc the lower row are hooked ; rjia'tof/aster is characterized by having no 

 dorsal, liut only the ventral row of bristles. Itoth forms lay large eggs singly, en- 

 closing them in protective capsules. It is, howe\ er, the asexual reproduction of these 

 worms wliich is so interesting. Tliere .appears in the midst of the body a little zone 

 of tissue, occupying at first less space than one of the segments between which it is 

 interpolated. The microscope shows that this tissue is of a very elementary character, 

 consisting of so-called embryonic or germinal cells. Gradually the tissue of this inter- 

 polated zone transforms itself into muscles, nerves, etc., and, growing meanwhile, it 

 forms in front a new tail jiiece to ]iatch out the anterior half of the worm, and be- 

 hind it forms a new head for the posterior half of the original body. The zone then 



