278 



CCELHELMINTHES 



operculum on one of the gills. Hydroidcs;* Proiula* ARENICOLID^E,* burrow 

 in sand, have gills on the sides of body. MALDANID^E (Clymene,*fLg. 263) have 

 extremely long segments and build tubes of sand. TEREBELLID^E (Tcrebella* 

 Amphitrite (fig. 261), numerous filiform tentacles and branched gills on the 

 anterior end. 



The ARCHIANELLID/E, which lack bristles and parapodia, must be 

 placed near the Polychaetae and are usually regarded as very primitive forms 

 which in structure and development (fig. 257) are of importance in the phylo- 

 genesis of the Annelids. Polygordius* 



Order II. Oligochaetae. 



The Oligochsetes are almost as preeminently fresh-water and terrestrial forms 

 as the Polychuetes are marine. They are in most respects simpler than their 

 marine relatives, apparently the result of degeneration. Eyes are rudimentary 

 or lacking, there are no palpi, cirri, or tentacles; gills are rare, but most striking 



FIG. 264. Aulophonis vagus* in tube of Pectinatella statoblasts (after Leidy). 



FIG. 265. Sexual organs of Lunihrlcus agricola (from Lang, after Vogt and 

 Yung). The seminal vesicles of the right side are removed, bm, ventral nerve 

 cord; bv and bl, ventral and lateral rows of setae; st, receptacula seminis; sb, seminal 

 vesicles of .the left side, connected with a median unpaired seminal capsule (sbii). 

 Enclosed in the latter are the testes (/z), and the seminal funnels (t), which lead into 

 the vas deferens (rd). o, ovaries; iv, ciliated funnels leading to oviducts with egg 

 capsule (e); di, dissepiments; 8-15, eighth to fifteenth segments. 



is the absence of parapodia, the bristles projecting directly from the body wall 

 (fig. 259). The chaetas may be regularly distributed around each somite (Pcri- 

 chceta) or gathered on the sides (Megascolex) or arranged in four groups so that 

 in the animal four longitudinal rows occur. The animals are hermaphroditic, 

 testes and ovaries lying in different somites. Usually the skin near the sexual 

 openirrgs is thickened by numerous glands, forming a clitellum (fig. 252), which 

 secretes the egg cocoons. and also functions in copulation, secreting bands which 

 hold the animals together so that the sperm from one passes into the receptac- 



