27S 



CCLLHEL^IIXTHES 



operculum on one of the gills. Hydroidcs:* Proliilj* Arexicolid.e,* burrow 

 in sand, have gills on the sides of body. M^ld.axid.e ^C/y«;i';;c,*fig. ^63) have 

 extremely long segments and build tubes of sand. Terebellid.e (Tfrcbflla.''' 

 Aiiiphitrilt i_hg. :bI^, numerous filiform tentacles and branched gills on the 

 anterior end. 



The ARCHIAXELLID.E, which lack bristles and parapodia, must be 

 placed near the PolvchaMa"' and are usually regarded as very priiuitive forms 

 which in structure and developiuent (tig. 257) are of importance in the pliylo- 

 giiitsis of the Annelids. Polygorjius* 



Order II. Oligochsetae. 



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

 as the Polvchanes are marine. Thev are in most respects simpler than their 

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

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



Fig. 264. — Ataoplio'iis z'agiis* in tube of PcctinalcUj statoblasts (after LeiJy"). 



.. . .... r-r— -^ sbi^r—A t— i — -;-, __ 



Fig. 265. — Sexual organs of Lumhricus agrkola (from Lang, after ^'ogt and 

 Yung). The seminal vesicles ..f the right side are removed, bin, ventrat nerve 

 cord; hv and W, ventral and lateral rows of seta'; si, receptaeula seminis; sb, seminal 

 vesicles of the left side, connceteil with a median unpaired seminal capsule [sbu). 

 Enclosed in the latter are the testes {ll^. and the seminal funnels [l^. which lead into 

 the vas deferens ivd). 0, o\aries; -,e, ciliated fuiuiels leading to oviducts with egg 

 capsule (c); di, dissepiments; S-ij, eighUi to lifteeuth segments. 



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

 (hg. 259). The ch;el;e may be regularly distributed around each somite (7'(t/- 

 cjuchi) or gathered on the sides {Mci^ascohw) or arranged in four groups so that 

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

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

 openings is thickened by numerous glands, forming a ditcllum (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 rcceptac- 



