274 INVERTEBRATE MORPHOLOGY. 



has 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- 

 chonella. 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 POLYZOA. 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. 



2. Order Ectoprocta. Anus outside the area enclosed by the lopho- 



phore. 



1. Suborder Phylactolcemata. Fresh-water forms ; lophophore 



usually horseshoe shaped ; epistome present. Frederi- 

 cella, Alcyonella, Lopliopus, Cristatella. 



2. Suborder Gymnolamata. Usually marine ; lophophore cir- 



cular ; no epistome. 

 Mouth of zoceciuin without bristles or operculum (Cydo- 



stomata). Crisia. 

 Mouth of zocecium usually surrounded by bristles which 



close over it (Ctenostomatd). Paludicella, Alcyonidium. 

 Mouth of zocecium provided with an operculum (Chilo- 



stomata). Membranipora, Buyula, Flnstra, Scnipocel- 



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. Lingnla, Crania. 



2. Order Testicardines. Shell-valves hinged ; peduncle when present 



protruding through perforation in the ventral shell ; anus 

 wanting. Terebralula, Waldheimia, Argiope, Rltynclio- 

 nella. 



