P L Y Z A 



171 



niul tlio disposition uf tin' tentacular arms (fig. 23) is the same in 

 Braohiopoda and Polyzoa. Tin 1 nephriiiia (oviducts) of Terebratula 



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

 tal ducts) of 1'horonis. The chief 

 difference between Polyzoa and 

 Braehiopoda consists in the special 

 development of the margin of the 

 cupped end of the body, into which 

 the lophophoro is sunk, as in IVdi- 

 cellina (see fig. 15, 13, e). This 

 up-standing margin is enormously 



Fig. 23. 



FIG. 23. Lophoplinre and epistome of young Terebratulina, showing the her 

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



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

 spirally coiled. (After Sloise.) 



FIG. 24. Larv.i of the Brachiopod Argiope (from Gegcnbaur, after Kowalewsky). 

 m, setigerous lobe; 6, setre; </, enteron. 



increased in the Braehiopoda, 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 Braehiopoda 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 Braehiopoda (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 larva? (fig. 25) have been compared to the segments of 

 Cha;topod worms by some writers ; and these, together with the 



presence of seta 1 , have been regarded as indicative of aflinity between 

 the Braehiopoda and ChtBtopoda (Morse). Hut it is sullieient, in 

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

 of the Chrctopoda follow one another along the primary oro-aiial 

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

 right angles to this (C'aldwell). 

 The Brachiopoda must be classified together with the Polyzoa 



FIG. 25. Surface views of ten stages in the development of Terebratulina. showing 

 the free-s\vimming larva and its mode of fixation (after Morse), c, lopliophoral 

 segment; tfi, thoracic segment; p, peduncular segment; rf.s deciduous seise. 



and Sipunculoidea in a phylum (Podaxonia) characterized by the 

 development of this secondary axis. 



_,_ ., ..._ me rvyzoa tn ifie llrmsli Museum (J^-'J, anu loyage 



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

 Marine Polyioa, London, 1880; (11) Smitt, Ki-itist FSrttclcning ofvtr Standi- 

 ' ffafs Bryozoa, 1864-68; (12) Heller, Die Bryozocn d. Jdriatisclim 



soma," Quart. Jour. Alicr. Set., April 18S5, 



