THE ANIMAL KINGDOM. 



the dorsal. Whether the anus has or has not become aborted in the Tes- 

 ticardines is a difficult question. Probability is, of course, in favour of the 

 former opinion. The walls of the digestive tract consist of an outer layer 

 of supporting substance lined by ciliated epithelium 1 . A ' liver ' lobe in 

 Argiope consists of 6-7 simple elongated caeca opening by a simple 

 common duct. The ducts are, however, usually ramified forming lobules. 

 The caeca are lined by a non-ciliated glandular epithelium. The food of 

 Brachiopoda consists of Diatoms, unicellular Algae, &c., collected by the 

 ciliated epithelium probably of both the cirri and brachial groove. Pro- 

 cesses of the outer, or supporting, tissue coat of the digestive tract serve to 

 suspend it in the body cavity. Their general disposition is as follows. A 

 median dorsal lamina connects it to the dorsal shell, while a ventral 

 lamina unites the oesophagus, stomach, and intestine, and is in Testicar- 

 dines attached also to the ventral end of the occlusor muscles, or in Crania 

 among Ecardines to the ventral valve. These laminae constitute the 

 ' mesentery ' of Huxley. The commencement of the stomach is connected 

 by two (Lingula) or three (some Testicar dines) ' gastro-parietal ' bands, 

 absent in Crania, to the dorsal shell at the attachment of the posterior 

 occlusor muscles, while a right and left ' ileo-parietal ' band tie it to the 

 side walls of the body behind the junction of the two mantle-folds. The 

 perivisceral portion of the coelome is large, and is broken up by the 

 viscera, muscles and supporting bands of the digestive tract. It is con- 

 tinued outwards into each lobe of the mantle as the pallial sinuses, which 

 are usually two or four in number in each lobe. The sinuses branch, as a 

 rule, in a manner characteristic of the genus or species, and in Lingula 

 anatina those branches which run radially and side by side towards the 

 free margins of the mantle lobes are close -set, thin-walled, and terminate in 

 small ampullae. 



A circumpallial sinus uniting the terminations of the pallial sinuses is 

 figured by Joubin in Distinct ; and is said by Hancock, but with some 

 doubt, to exist in Waldheimia australis, &c. Other extensions of the 

 coelome are the sinuses at the sides of the oesophagus, which are connected 

 to a canal coursing along the bases of the cirri in the lophophore oi Argiope, 

 or to two canals in the lophophoral arms of Crania, &c. The coelomic 

 epithelium is ciliated partially or wholly. 



The existence of a circulatory system has been denied by most modern 

 authorities, but the recent investigations of Blochmann prove its existence, 

 and, to a certain extent at least, as it was described by Hancock, in a large 



1 Beyer describes the wall of the tract in Lingula pyramidata as consisting of three layers: (i) 

 a layer of supporting tissue; (2) one of granular small cells; (3) one of ciliated cells. Joubin 

 figures the epithelium in Crania as consisting of extremely narrow and long ciliated cells with basal 

 nuclei. It is possible that Beyer's second layer corresponds to the basal nuclei or to granules in the 

 bases of the cells. 



