316 



C(ELHELMINTHES. 



species (Megascolex australis four feet long). Our species belong to 

 Lumbricus* Allobophora*; Perichceta* has been introduced from the 

 tropics; Diplocardia * with double dorsal blood-vessel. Most species agree 

 in habits; they burrow through the earth, swallowing the humus and 

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

 are continually bringing the deeper parts to the surface, and thus do great 

 good. Contrary to oft-repeated statements, earthworms occurred in our 

 prairies and plains when first broken up by the plow. Details of the 

 reproductive organs of one species are shown in fig. 286. These vary 

 greatly and are largely used in classification. 



Sub Class II. Gephyrcea. 



The exclusively marine Gephyraea are distinguished at the first 

 glance from the Chaetopoda by the 

 entire absence of segmentation. The 

 body is oval or spindle-shaped, circular 

 in section. The mouth, at the ex- 

 treme anterior end, is either surround- 

 ed by a circle of tentacles (fig. 287} 

 and is retracted together with the 

 anterior end of the body by internal 

 retractor muscles, or is overhung by a 



FIG. 287. FIG. 288. 



FIG. 287. Anatomy of Phascalosoma gouldi (orig.). a, anus; a, anterior retractors 

 d, digestive tract; g, gonads; m, mouth; n, nephridia; TIC, ventral nerve cord 

 pr, posterior retractors. 



FIG. 288. Larva (trochophore) of JSchiurus. (After Hatschek.) a, anus; d, intestine 

 hw, postoral cilia; fcra, protonephridia; m, mouth; mes, mesoderm bands with indi- 

 cation of segments; n, ventral nerve cord; sc, oesophageal commissure; sp, apical 

 plate; vto, preoral ciliated band. 



