ECHINODEHMA. 329 



(7) The Ch,et<)Pod Annelids have segmented bodies, the segmentation 

 showing itself in ringing of the body wall and in the separation of the 

 coitem into a series of pouches by transverse septa and the metamerio 

 arrangements of blood-vessels, ganglia, and excretory organs. 



(8) The Uh^topoda are distinguished from other annelids by the 

 chseta? (usually four bunches in a somite) arising in special follicles. The 

 chietas are few in tlie hermaphroditic Oligochaeta;, numerous and borne on 

 special parapodia in the Polychsetse. 



(9) The GephyRjEA are closely related to the ChiBtopoda. They are 

 saccular, with a crown of tentacles or well-developed preoral lobe. They 

 have largely or entirely lost the segmentation. Evidence of segmentation 

 appears in some cases in development and in the ventral nerve cord and 

 nephridia. 



(10) The HiRUDiNEi are hermaphroditic Annelida which lack chsetsB 

 but have sucking discs. Their flattened bodies, rudimentary coelom, and 

 rich body parenchyma give them a certain similarity to the Plathelmin- 

 thes. 



(11) The Hirudinei have either a protrusible pharynx (Rhynchobdella) 

 or three toothed jaws (Gnathobdella). To tlio latter belongs the medici- 

 nal leech (Hifiulo medicinalis). 



(13) The PoLYZOA are like the Hydrozoa in being colonial and having a 

 circumoral crown of tentacles. They are distinguished by the complete 

 alimentary canid, the large ecelom, and the ganglionic nervous system. 



(13) The Phoronidea are closely like the Polyzoa. 



(14) The Brachiopoda liave a bivalve shell, the valves being dorsal and 

 ventral. 



(15) The body cavity is divided by two septa into three (paired) cham- 

 bers, of which one, rarely two, are provided with nephridia. 



(16) Most brachiopods are attached by means of a stalk. Tliey are 

 divided into Ecardines, without a hinge and with anus, and Testicardines, 

 with a hinge and no anus. 



PHYLUM A'. ECniXODERMA. 



Tlio Ecluiiodemia are separated from most otlier animals by 

 tlieir radial symmetry, Imt recall in this respect the C'leleiiterata, 

 a fact which led to their inclusion by Cnvier in the gronji 

 'Radiata.'a view of their relationships which was set aside by 

 Leuckart on account of their different structure, especially the 

 presence of a ecelom. In fact the radial symmetry of the echino- 

 derms has a different value, for while in the Ccelenterata the 

 number four or six (apparently derived from four) is fundamental, 

 Echinoderma are, with few exceptions, five-radiate. Further, the 

 radial symmetry of the Ccelenterata is primitive, that of the 

 Echinoderma, as development shows, is derived from the bilateral 



