III. ANNELIDA: GEPHYR^A 



279 



After impregnation the eggs are usually enclosed in 



ulum seminis of tlie other. 



cocoons. 



Sub Order I. LIMICOLA (Microdrili). Mostly fresh-water. The 



TuBiFiciD^, in consequence of the red blood, when present in large numbers 



color the bottom red. They form tubes in the 

 mud. Tubifex,'^- ClilelUo irroratus*- common on 

 seashore. Naidid^, transparent forms living on 

 water plants, reproduce asexually. Dero* and 

 Aulophorus* (fig. 264) have gills around the anus. 

 Enchytr^id^; Pachydrilus. Discodeilid^ 

 (Myzobdella), parasitic. Sub Order II. TERRI- 

 COLA (Macrodrili). Terrestrial; the earthworms, 

 our species of moderate size, in the tropics large 

 (Megascolex australis four feet long). Lumbricus ,''' 

 Allobophora*; Diplocardia* with double dorsal 

 blood-vessel; Perichaia'* introduced from the 



Fig. 266. Fig. 267. 



Fig. 266. — Anatomy of Phascolosoma gouldi (orig.). a, anus; a, anterior retractors; 

 d, digestive tract; g, gonads; ni, mouth; «, nephridia; nc, ventral nerve cord; pr, posterior 

 retractors. 



Fig. 267. — Larva (trochophore) of Echiurus (after Hatschek). a, anus; d, 

 intestine; hw, postoral cilia; kn, protonephridia; m, mouth; mes, mesoderm bands with 

 indication of segments; 11, ventral nerve cord; sc, cesophageal commissure; sp, apical 

 plate; vw, preoral ciliated band. 



tropics. Most species burrow through the earth, swallowing the humus and 

 casting the indigestible portions on the surface. They loosen the soil and con- 

 tinually bring the deeper parts to the surface. Details of the reproductive 

 organs of one species in fig. 265. These vary and are used in classification. 



Stib Class II. Gephyraa. 



The exclusively marine GephyrKa are distinguished at the first glance 

 from the Cha;topoda by the absence of segmentation. The body is oval 



