318 ARTICULATA. 



it does not appear to resemble the trochosphere larvae so far described, or 

 the more typical larvae of the Chsetopoda, in that the ring of tentacles, which 

 is probably, as already mentioned, derived from the ciliated ring shewn in 

 fig. 137, is post-oral, and not prce-oral. The ring of tentacles is like the 

 ring in Actinotrocha (the larva of Phoronis) amongst the Gephyrea. 

 Although there is no doubt a striking resemblance between the tentacular 

 disc of a larval Brachiopod and the lophophore of a Polyzoon, which has 

 been pointed out by Lankester, Morse, Brooks, etc., their homology is 

 rendered, to my mind, very doubtful (i) by the fact that the lophophore is 

 prae-oral in Polyzoa 1 and post-oral in Brachiopoda ; and (2) by the fact that 

 the concave side of the lophophore is turned in nearly opposite directions 

 in the two forms. In Brachiopods it is turned dorsalwards, and in phylacto- 

 laematous Polyzoa ventralwards. 



The view of Morse, that the Brachiopoda are degraded tubicolous 

 Chaetopods, is not so far supported by any definite embryological facts. 

 The development of the tentacular ring as well as its innervation from the 

 sub-oesophageal ganglion prohibit us, as has been pointed out by Gegenbaur, 

 from comparing it with the tentacles of tubicolous Chaetopoda. 



BIBLIOGRAPHY. 



(325) W. K. Brooks. "Development of Lingula." Chesapeake Zoological 

 Laboratory, Scientific Results of the Session of 1878. Baltimore, J. Murphy and Co. 



(326) A. Kowalevsky. "Development of the Brachiopoda." Protocol of the 

 First Session of the United Sections of Anatomy, Physiology, and Comparative Ana- 

 tomy at the Meeting of Russian Naturalists in Kasan, 1873. (Russian.) 



(327) H. Lacaze Duthiers. " Histoire de la Thecidie." Ann. Scien. Nat. 

 etc. Ser. 4, Vol. xv. 1861. 



(328) Morse. " On the Early Stages of Terebratulina septentrionalis." Mem. 

 Boston Soc. Nat. History, Vol. II. 1869, also Ann. 6 Mag. of Nat. Hist., Series 4, 

 Vol. VIII. 1871. 



(329) "On the Embryology of Terebratulina." Mem. Boston Soc. Nat. 



History, Vol. Hi., 1873. 



(330) " On the Systematic Position of the Brachiopoda." Proceedings of 



the Boston Soc. of Nat. Hist , 1873. 



(331) Fritz Muller. " Beschreibung einer Brachiopoden Larve." Muller's 

 Archiv, 1860. 



1 For the ectoproctous Polyzoa it might be held that the ciliated ring of tentacles 

 is post-oral, but the facts of development recorded in the previous chapter appear to 

 me to shew that this view is untenable. 



