P L Y Z A 



171 



and the disposition of the tentacular arms (fig. 23) is the same in 

 Brachiopoda and Polyzoa. The nephridia (oviducts) of Terebratula 

 have a position and relations similar to those of the nephridia (geni- 

 tal ducts) of Phoronis. The chief 



difference between Polyzoa and 

 Bracliiopoda consists in the special 

 development of the margin of the 

 cupped end of the body, into which 

 the lophophore is sunk, as in Pedi- 

 cellina (see fig. 15, B, e). This 

 up-standing margin is enormously 



Fig. 23. 



Fig. 24. 



FIG. 23. Lophophore and epistome of young TerebratuliDa, showing the hone- 

 shoe shape; the arms are turned in the direction the reverse of that taken by 

 the lophophore-arms in Polrzoa (see fig. 4). In later growth they will become 

 spirally coiled. (After Mo:se.) 



Fio. 24. Larv.1 of the Brachiopod Argiope (from Gegenbaor, after Kowalewsky). 

 m, set geroua lube; b, setae ; d, enteron. 



increased in the Brachiopoda, so as to form a voluminous hood or 

 collar, which surrounds the large tentacular arms, and forms a pro- 

 tective chamber for them. It is notched right and left so as to be 

 divided into two lobes, and on its surface is developed a horny or a 

 calcareous shell in two corresponding moieties. Until recently it 

 was held (see Lankester, 17) that both Brachiopoda and Polyzoa 

 were modifications of the Molluscan type, and the Brachiopods" 

 collar was identified with the pallial fold of Mollnsca. The resem- 

 blance of the two structures must now be considered as purely 

 homoplastie, and not as having any real morphological (homo- 

 genetic) significance. 



The larvae of the Brachiopoda (figs. 24, 25) are as exceptional and 

 difficult of interpretation as those of Polyzoa, but no attempt has 

 been yet made to show that the one can be reduced to a common 

 form with the other. The three segments presented by some 

 Brachiopod larvae (fig. 25) have been compared to the segments of 

 Chaetopod worms by some writers ; and these, together with the 



presence of set*, have been regarded as indicative of affinity between 

 the Brachiopoda and Chaetopoda (Morse). But it is sufficient, in 

 order to dispose of this suggestion, to point out that the segments 

 of the Chaetopoda follow one another along the primary oro-ana| 

 axis, whilst those of Brachiopoda are developed along an axis at 

 right angles to this (Caldwell). 

 The Brachiopoda must be classified together with the Polyzoa 



Fio. 25. Snrf ace views of ten stages in the development of Terebratulina, showing 

 the free-swimming larva and its mode of fixation (after Morse), e, lophophoral 

 segment; th, thoracic segment; p, peduncular segment; ds, deciduous setae. 



and Sipunculoidea in a phylum (Podaxonia) characterized by the 

 development of this secondary axis. 



Bibliography. (I) 3. Vanghan Thompson, Zoological Researches, Memoir T., 

 "On Polyzoa, a new animal, an inhabitant of some Zoophytes," Ac., 1830; (2) 

 Ehrenberg, Abhandl. d. t. Atad. a. Katunciss. tu Berlin, 1*34; (3) Henri Milne- 

 Edwards, Rechercha anatomiquts, physiotogiques, ft toologiqua lur let Polypiert 

 de France, 8vo, 1841-44; (4) Altaian, The. British Frahxater Polyioa, Ray 

 Society, 18-56 ; (5) Jolllet, " Bryozoaires des cotes de France," Arch. d. Zool. 

 experim^vol. Ti., 1877; (6) Caldwell, Proceedings of the Royal Society. 1883; 

 (7) Lankester, " Rhabdopleura," Quart. Jour. Mitr. Sci., 1884; (8) Nitsche, 

 Zeilschr. far Kits. Zoologie, 1869, and supplement volume, 1876 ; (9) Busk, 

 Catalogue of the Marine Pofyzoa in the British tfuseum (1852X and Voyage 

 of the ' Challenger" " Report on the Polyzoa," vol. x. ; (10) Hincks. British 

 Marine Polyzoa, London, 1880; (11) Smitt, Kritist Fortectxing 6/rer Standi- 

 narient Haft Bryozoa, 1864-68; (13) Heller, Die Bryoioen d. Adrialischm 

 Ueeret, 1867: (13) Ehlers, " Hypophorella expanse," Abhandl. d. Umig. Geiellsch. 

 Gottingen. xxi., 1876; (14) Barrels, Annales dei Sciences Saturellet, vol. ix., 

 1880; (15) Balfour, Comparative Embryology, London. 1880, vol. i., p. 242 ; (16) 



soma," Quart. Jour, tlicr, Sci., April 188S. 



(E. R. L.) 



