WORMS. 223 



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

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

 found only in Germany. 2. Tubificid^. The common and graceful TuUfex makes 

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

 digging up 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 ; they will 

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

 turbance causes the frightened woi-m to jerk back into its domicile. The animal is long 

 and slender as a thread, somewhat reddish in color and transparent. With a lens 

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

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

 hair-shaped ones, form the upper row. Along the New England coast the allied genus 

 Vlitellio is common, being, unlike TvUfex, an inhabitant of the ocean ; it is found, in 



Fig. 214. — Phreoryctes meiikeanus, 



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

 near high-water mark. 



The members of the third family, ENCHYTE^iDiE, live in the earth, rotten woods, 

 waters of swamps and the ocean. The red-blooded Pachydrilus may be taken as 

 typical ; it being a common marine genus. The last family, the Naid^, comprises 

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

 and CluBtogaster, having been studied again and again by naturalists during the last cen- 

 tury and a half, their wonderful reproduction by transverse di\'ision always possessing 

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

 tured by scooping blindly through the plants growing in fresh water, among which 

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

 from the head. Very common is the Nais proboscidea., which has a relatively immense 

 appendage " proaking out before its eyes." This long trunk is used to feel the way. 

 Another member of the same genus, however, has a simple rounded head. The genus 

 itself is easily i-eeognized by the fact that the upper row of bristles on each side are 

 hair-like, while the lower row are hooked ; Chcetogaster is characterized by having no 

 dorsal, but only the ventral row of bi-istles. Both forms lay large eggs singly, en- 

 closing them in protective capsules. It is, however, the asexual reproduction of these 

 worms which is so interesting. . There appears in the midst of the body a little zone 

 of tissue, occupying at first less space than one of the segments between whicli 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, gi-owing meanwhile, it 

 forms in front a new tail piece to patch out the anterior half of the woim, and be- 

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



