216 SUMMARY OF CURRENT RESEARCHES RELATING TO 



been described by Hancock ; the vessels appear to be only slits in tbe 

 tissue ; the blood-corpuscles are large in comjjarison with the other 

 cells of Argiope, " which, like all Brachiopod cells, are extremely 

 small." Respiration appears to be effected by the mantle, and especially 

 in the region of the perforate shell, where a large area is constantly 

 exposed to the currents of water which are set up by the action of the 

 ciliated tentacles. 



After describing the muscular and nervous systems, the author 

 comes to the female organs, no male having been found by him. 

 There are two pairs of ovaries, one of which is not constantly present ; 

 each appears to be formed of a membrane continuous with the body- wall, 

 and covered by epithelium continuous with that of the body-cavity ; 

 each ovum is surrounded by a very delicate nucleated capsule. The 

 ripe eggs fall into the body-cavity, where they are taken up by the 

 inner end of the oviduct, whence they pass into the brood-pouches. 

 These last are invaginations of the lateral body-wall. By invagina- 

 tion three cavities are formed in the embryo, which at first com- 

 municate at the end near the blastopore, but subsequently become 

 shut off from one another. The central cavity, which is enteric, is, 

 throughout the larval life, without a mouth or anus. The two lateral 

 cavities give rise to the body-cavity, and their walls form the muscles 

 and other mesoblastic structures ; sometimes these walls are so much 

 in contact that the body-cavity is obliterated in many places. The 

 embryo becomes divided into two segments, of which the anterior 

 soon becomes again divided; four symmetrically arranged eye-spots 

 now appear, and four bundles of small bristles are soon afterwards 

 developed on the second segment. The stalk of the adult is formed 

 from part of the third segment. A little later the larva escapes from 

 its mother and swims about by the aid of cilia ; the setae and the red 

 colour have probably a protective function. 



The author discusses the views of Morse and Kowalevsky, that the 

 Brachiopoda form an order of Vermes closely allied to the Chaetopoda, 

 against which he points out that the " segments " of the larva do not 

 seem to have the value of true metameres, but to be due simply to the 

 formation of the shell from the central region of the body ; there is no 

 trace of any segmentation of the mesoderm, and no organ exhibits 

 serial repetition. The Brachiopod differs from the Chsetopod larva in 

 having an alimentary canal which is not curved, nor divided into three 

 regions, nor provided with mouth or anus ; the body-cavity is but 

 feebly developed, and there is no provisional renal organ. Brooks" 

 adopts the view of Huxley and Hancock that the Brachiopoda are allied 

 to the Polyzoa ; but Shipley points out that (a) Balfour has already 

 rendered very doubtful the homologies of the lophophore ; (6) that the 

 characteristic position of the nerve-ganglia of Brachiopods which 

 remain in the ectoderm, is without parallel in the Polyzoa ; (c) there 

 are no proper resemblances between their larvae ; and (d) the Polyzoa 

 become fixed by the prseoral, the Brachiopods by their aboral 

 extremity. 



Van Bemmelen would ally the Brachiopods to the Chsetognatha, 

 basing his views chiefly on resemblances in histological structure ; 



