514 Arthur E. Shipley 



of setae. I do not coiisider the »segmeuts« of the larva to have the vahie 

 of true metameres, they are simply the result of the formation of the 

 shell frorn the centrai region of the body, thus necessarily dividing the 

 body into three parts, viz. , one lying before the shell-forming region. 

 the shell-forming region itself, and a third part posterior to it. In the 

 larva there is no trace of segmentation of the mesoderm , and none of 

 the Organs shew the least trace of serial repetition; and with the ex- 

 ception of the second pair of oviducts in Rhyuchonella there is no trace of 

 segmentation in any adult Brachiopod. Balfour has already pointed 

 out that the formation of the segments at the cephalic end of the body, 

 as in Cestodes »renders it probable that they are not identical with the 

 segments of a Chaetopod«. The larva differs from the characteristic 

 Chaetopod larva in the follo wing particulars. 1 ) The alimentary canal is 

 not curved, nor divided into three regious, neither mouth nor anus is 

 present ; 2) the body cavity is but very slightly developed, it is not tra- 

 versed by muscular Strands, there is no connection between the nerve 

 ganglion and the alimentary canal; 3) there is no pro visionai renai orgau. 



Finally as is shewn in fig. 35 we must consider the full grown larva 

 of Argiope to consist of four regions and not of three like the larva of a 

 Chaetopod, and these four regions do not correspond with the four describ- 

 ed by Lacaze-Duthiers in the larvai Thecidium. 



In the adult structure there is no resemblance in any system of 

 Organs between the two classes except the possession of setae, but these 

 structures are not confined exclusively to the two classes in question. 



Brooks in his article upon the development of Lingula, has upheld 

 the relationship between Brachiopoda and Polyzoa, which was urged by 

 both Huxley und Hancock. 



The most striking points of resemblance in the adult anatomy are 

 the Position of the chief nervous system and the possession of a lopho- 

 phore. With regard to the first point, the nervous system of both classes 

 consistslike that of the majority of Invertebrates of a circum-oesophageal 

 nerve ring upon which nerve ganglia are developed, the point of resem- 

 blance lying in the fact that the sub-oesophageal ganglion of Brachio- 

 pods is larger than the supra-oesophageal , while in the Polyzoa the 

 latter is not developed or only to a very slight extent. The characteristic 

 Position of the chief nerve ganglia of Brachiopoda which remain in the 

 ectoderm has no parallel in Polyzoa. 



Balfour has in his Comparative Embryology already pointed out 

 that the homology of the lophophores »is rendered very doubtful (Ij by 



