268 INVERTEBRATE MORPHOLOGT. 



Another view, however, which has had ardent supporters is that 

 which recognizes a relationship between the Polyzoa and Phoronis. There 

 is a lophophore in both, likewise a U-like bending of the digestive 

 tract, and the nephridia of Phoronis may be considered comparable to 

 those of the Endoprocta. But here the similarity ceases. The anus in 

 Phoronis is outside the limits of the lophophore and is comparable in 

 position with that of the Ectoproota, a point which tells against this 

 phylogeny since these forms have been shown to be less primitive than the 

 Endoprocta. If, however, this phylogeny should prove to be correct, it 

 will show a descent for the Polyzoa from metameric Annelids, through the 

 Gephyrea, since it is to this group that Phoronis seems to be most nearly 

 related. 



III. Class Brachiopoda. 



The Brachiopoda constitute a very well-defined group 

 whose present poverty in species is in striking contrast to its 

 great development during Palaeozoic times. Like the Poly- 

 zoa they possess a tentaculate lophophore (Fig. 120, Ip) which 

 usually takes the form of two exceedingly elongated, some- 

 times spirally- coiled, arm-like processes projecting, one on 

 either side, from the anterior portion of the body, and fur- 

 nished upon their outer or posterior border with tentacles. 

 The body is usually somewhat short and stout, and prolonged 

 posteriorly into a peduncle (pe) or stalk which is in some 

 cases at least provided with adhesive papillae and serves as 

 an anchor. 



The most characteristic feature of the Brachiopoda is, 

 however, the presence of a bivalved shell (Fig. 119) similar 

 to that of a bivalve Mollusk, with which forms the Brachio- 

 pods were until comparatively recently, associated. From 

 near the base of the peduncle, upon the dorsal and ventral 

 surfaces of the body, a fold of the body-wall is found, which 

 contains a cavity in communication with and indeed in reality 

 a portion of the coelomic cavity. These two folds are of suffi- 

 cient size to enwrap or enclose the body and the lophophore 

 and are termed the mantle-lobes (Fig. 120, m), the space between 

 them and the body being known as the mantle-cavity. They 

 subserve largely if not entirely the function of respiration 

 the portion of the coelom which they contain being more or 

 less divided up into a system of lacunae through which the 



