The alimentary tract after the obliteration of the blastopore forms a closed sack, which becomes subsequently placed in communication with the exterior by the stomodæal invagination. The liver is formed as a pair of dorsal outgrowths of the mesenteron. From Brooks' observations on Lingula it would appear that the primitive mesenteron forms the stomach of the adult only, and that the intestine grows out from this as a solid process: this eventually meets the skin, and here the anus is formed. In the Articulata the mesenteron is aproctous. The origin of the body cavity as paired archenteric diverticula has already been described. Its somatic wall becomes in Lingula ciliated, and its cavity filled with a corpusculated fluid, as in many Chætopods. It is eventually prolonged into the dorsal and ventral mantle lobes as a pair of horn-like prolongations into each lobe, which communicate with the body cavity by large ciliated openings. Some incomplete observations of Brooks on the development of the nervous system in Lingula shew that it arises in the embryo as a ring round the oesophagus with a ventral sub-oesophageal (fig. 138 _q_), and two lateral ganglia, and two dorsal otocysts. The ventral ganglion is formed as a thickening of the epiblast, with which it remains in continuity for life. The remainder of the ring grows out from the ventral ganglion as two cords, which gradually meet on the dorsal side of the oesophagus. _General observations on the Affinity of the Brachiopoda._ The larva of Argiope, as has been noticed by many observers, has undoubtedly very close affinities with the Chætopoda. It resembles, in fact, a mesotrochal larval Chætopod with provisional setæ (_vide_ Chapter on Chætopoda). Lacaze Duthiers' observations point to the lobes of the larva not being true segments, and certainly the mesoblast does not in the embryo become segmented as it ought to do were these lobes true segments. If this view is correct the larva is to be compared to an unsegmented Chætopod larva. In Rhynchonella, however, indications of two segments are afforded in the adult in the two pairs of segmental organs.