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 Terehratula 

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

 tal ducts) of Phoronis. The chief 

 difference between Polyzoa and 

 Brachiopoda 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, c). This 

 up-standing margin is enormously 



Fig. 23. Fig. 24. 



Fig. 23. — Lophophore and epistome of young Terebratulina, showing the horse- 



Bhoe shape; tlie arms are turned in the direction the reverse of that tal^en by 



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



spirally coiled. (After Morse.) 

 Fig. 24. — Larva of the Brachiopod Argiope (from Gegenbaur, after Kowalevfslty). 



m, setigerous lobe; d, setse ; 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. tJntil 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 Mollusca.' The resem- 

 blance of the two structures must now be considered as purely 

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

 genetic) significance. 



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

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

 been j'et made to show that the one can be reduced to a common 

 form with the other. The three segments presented by some 

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

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



presence of setse, have been regarded as indicative of affinity between 

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

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

 of the Chsetopoda follow one another along the primary oro-anaj 

 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 



Fig. 25.— Surf ace views of ten stages to the development of Terebratulina, showing 

 the fi-ee-swimming larva and its mode of fixation (after Morse), c, lophophoral 

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



and Sipunculoidea in a phylum (Podaxonia) characterized by the 

 development of this secondary axis. 



Bibliography.— (1) J. Vanghan Thompson, Zoological Researches, Memoir v., 

 " On Polyzoa, a new animal, an inhabitant of some Zoophytes," 4c., 1830; (2) 

 Ehrenberg, Ahhandl. d. k. Akad. d. Naturwiss. zu Berlin, 1834; (3) Henn Milne- 

 Edwards, Recherches anatomiques, physiologiques, et zoologiques sur les Polypiers 

 de France Bvo, 1841-44; (4) Allman, The British Freshwater Polyzoa, Ray 

 Society, 1856 ; (5) JoUict, " Bryozoaires des cotes de France," Arch. d. Zoo!, 

 expirim vol. vi., 1877; (6) Caldwell, Proceedings of the Royal Society, 1883; 

 (7) Lankester, " Rhabdopleura," Quart. Jour. Mia: Set, 1884; (8) Nitsche, 

 Zeitschr. fur mss. Zoologie, 1869, and supplement volume, 1876 ; (9) Busk, 

 Catalogue of the Marine Polyzoa in the British Museum (1852), and Voyage 

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

 Marine Polyzoa, London, 1880; (11) Smitt, Kritisic Forteckning Bfver Skandi- 

 naviens Hafs Bryozoa, 1864-68; (12) Heller, Die Bryozoen d. Adrtaltschm 

 iTeeres, 1867; (13) Ehlers, " Hypophorella expanse," Abhandl. d. kdntg. Gesellsch. 

 Oottingen. Xii., 1876; (14) Barrois, Annates des Sciences Naturelles, ™1. Jx., 

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

 Morse " On the Systematic Position of the Brachiopoda," Boston Soc, Nat. Hist., 

 vol XV 1873 ; (17) Lankester, " Remarks on the AfBnitics of Rhabdopleura, 

 Quart. Jour. Micr. Sci., vol. xiv., new series, 1874; (18) Harmer, "On Loxo- 

 soma," Quart. Jour. Micr. Sci., April 1886. (E. R. L.) 



