EXCEETOKY OKGANS OF BKACHIOPODA. 



313 



evoii though their f Linction be modified. There are either one or two 

 pairs of them. When there are four, two of them belong to tho 

 so-called dorsal, and two to the ventral half (Rhynchonella) ; this 

 points to tho presence of two metauieres, which have disappeared in 

 this portion of the body. The dorsal ones are absent in Lingula 

 and the Terebratulida. The canals, which generally open to tho 

 exterior near the base of the arms, open into the ccolom, after having 

 taken a bent course, by funnel-like enlargements (Fig. 166, r), 

 which are distinguished by their radially-arranged folds. This 

 orifice passes through the ileoparietal band, and is thus directed 



m il 



Fig. 166. Lateral view of the organisation of Waldheimia australis. D Dorsal, 

 V Ventral surface. P Stalk. II Spirally-coiled arms, hr Branchial filaments, c An- 

 terior wall of the perivisceral cavity, d CEsophagus. d' Mid-gut. h Liver, h ' Its 

 openings into the mid-giit. r Internal orifice of the right oviduct (some folds only 

 of the left oviduct can be seen), e Brachial canal, m m' m" m* Muscles to move 

 the valves of the shell (after A. Hancock). 



towards the pericardial cavity. The ileoparietal band resembles 

 therefore, in its relation to the internal orifice, a dissepiment of the 

 Vermes (cf. supra, § 243). 



Although the walls of these canals appear to be glandular in 

 character, owing to the possession of projections, villous processes, 

 or folds, we know nothing of their function, save that they have a 

 relation to the generative organs ; so that they appear to form an 

 oviduct, and have indeed been hitherto regarded as being such. And 

 as the looped-canals serve as parts of the generative apparatus in 

 the Gephyrea and Annelides, it is not to be wondered at that they 

 have the same relations in the Brachiopoda ; but this does not 

 exclude the possibility of their having an excretory function also. 



