274 INVEBTEBBATE MOBPHOLOGT. 



lias been simply a bending of the digestive tract and a migration forwards 

 of the anus. 



If this be the correct way of regarding the matter, then there is no 

 reason for disputing the homology of the dissepiments of the Brachiopoda 

 with those of the Annelida, and the idea that they represent a metamerism 

 is borne out by the arrangement of the two pairs of nephridia of Rhyn- 

 clionella. The question is then. Does the metamerism of the Brachiopods 

 indicate a descent of the Prosopygia from metameric ancestors, i.e., from 

 Annelids through Gephyrean-like forms, or is it a structural feature inde- 

 pendently acquired by the Brachiopods ? The evidence at our disposal is 

 not sufficient for the solution of this problem, and all that can be main- 

 tained is that a very close relationship exists between the Polyzoa and the 

 Brachiopoda. 



SUBKINGDOM METAZOA. 



TYPE PROSOPYGIA. 



I. Class PoLtzoA.— Small, usually colonial forms ; lophophore circular or 

 horseshoe-shaped ; no bivalve shell ; no mantle-lobes. 

 1. Order Endoprocta. — Mouth and anus both within the area enclosed 

 by the lophophore. Loxosoma, Pedicellina, Ascopodaria, 

 Urnatella. 

 3. Order^etojjrocto.— Anus outside the area enclosed by the lopho- 

 phore. 

 1. Suborder Phylactolamata.—'Fresh-wa.teT forms ; lophophore 

 usually horseshoe shaped ; epistome present. Prederi- 

 cella, Alcyonella, Lophopus, Cristatella. 

 3. Suborder GymnolcBmata. — Usually marine ; lophophore cir- 

 cular ; no epistome. 

 Mouth of zocecium without bristles or operculum {Cydlo- 



stomata). Crista. 

 Mouth of zocecium usually surrounded by bristles which 

 close over it {Ctenostomata) . Paludicella, Aleyonidium. 

 Mouth of zocecium provided with an operculum {Chilo- 

 stomata). Membranipora, Bugula, Fliistra, Scrupocel- 

 laria. 

 II. Class Brachiopoda. — Non-colonial and of moderate size ; lophophore 

 usually arm-like and coiled into a spiral ; mantle-lobes 

 and bivalve shell present. 

 1. Order Ecardines. — Shell-valves not hinged ; peduncle protrudes 



between the valves ; anus present. Lingula, Crania. 

 3. Order Test i car dines. — Shell-valves hinged ; peduncle when present 

 protruding through perforation in the ventral shell ; anus 

 wanting. Terebratula, Waldheiinia, Argiope, Rhyncho- 

 nella. 



