WORMS: 215 



cud of the body, jiarticiilarly the region of tlie cesophagus, is very much thickened ; in 

 ( 'h(jttosoma this thickening ends abrujttly posteriorly. The body shows fine transverse 

 lines, and has hairs or bristles upon the back. Tlie mouth is ^jjj^^ 



surrounded by tln-ee lips. The male has two hooks around 

 tiie genital aperture, which are very similar to the so-called 

 si)icuku of nematod worms. The most singular and charac- 

 teristic feature of Chmtosoma, however, is a double row of 

 short rods on the ventral side, just in front of the anal open- 

 ing ; each rod has a knob at the free end. Nothing is known 

 of the life history of these interesting forms. Hitherto they 

 have been observed in Euro])e only, but it seems probable 

 that they will yet be discovered in America. 



The second type, the Desmoscolecidjs, is also imper- 

 fectly known. It ])resents some indications of segmentation 

 of the bo<ly, but whether it is really jointed like a true anne- 

 lid is \ ery doul)tful. We cannot do more than give a briet 

 (lescrijitiou of a. typical »\i(n:'KS, Desmoscolex minutus. The 

 animal lias a head-like enlargement of the anterior end of 

 ihe licidy, and, behind that, a series of protuberant rings, pro- 

 ducing an appearance of segmentation. The head carries 

 two pairs, and each ring (save the eleventh and fifteenth) a 

 single pair of bristles, which Greef states are used as locomo- 

 tive organs. The sexes are distinct, and nuiy be recognized 

 l>y secondary external sexual characters. Three or four eggs 

 are laid at a time, and borne about by tlie female for somt 

 while. The animal is marine. 



Class VII. — NEMER TEA. 



The nemertean worms are free-living animals, usually very 

 nuich elongated in shape, but especially characterized by an 

 enormously long slender proboscis, which when at rest, is 

 withdrawn into the body, but is thrown out upon slight 

 ])rovocation. When one of these animals is captured, the 

 jjroboscis is often broken off and might readily be mistaken 

 for a second worm, for it is a long filament, which maintains 

 its autonomic contortions for a considerable period. The 

 Nemertea were long classed with the Turbcllaria, but the 

 union with the latter was based upon gross misconceptions, j& 

 and we now know that they must stand as an independent Iw 

 class, having more affinity with the true .annelids than with S, 

 the plathelminths. 



We may take the well known genus Tetrastennna as #■ 



tyjiical of the class, although most of the forms are very < '.\' ' ' ■ . 



much larger. The species represented in our illustration . ■ - 



is only two millimetres long, while some nemerteans ex- ' ' ' ' 



ceed a foot in length. In TitrantciiiDia the opening of ~~^ 



the mouth, and also that of tlu^ canal, in which the re- FiQ.-i<n.—Tetrastemmaohscurn. 



