BRACHIOPODA. 493 



The mouth {fig. 186, ?0 ^^ ^^ Terebratula is situated in the middle 

 line, about one-third of the length of the shell from the hinge ; it 

 opens downwards, towards the ventral valve, at the base or beginning 

 of the passage formed by the spiral brachial fold and the converg- 

 ing fringes of the brachial spire;, it has a tumid and sub-bilobed 

 upper or anterior lip, and a thinner and broader lower or posterior 

 lip, which is attached to the basal portion of the fringed arms 

 uniting the central portions. The swollen margins of the mouth 

 are formed by both muscular fibres and secerning cells : there are 

 no rudiments of a maxillary or dental apparatus. The organic 

 molecules subserving the nutrition of the Brachiopods are brought 

 by ciliary action within reach of the mouth, are there seized and 

 swallowed. In Orhicula the mouth is opposite the centre of the 

 perforated valve ; in Lingula it is nearer the fore part of the 

 sheU. The oesophagus in Terebratula is short, of uniform diameter, 

 has a delicate membranous outer tunic, a muscular coat, and a thicker 

 epithelial lining than that of the rest of the alimentary canal. It 

 inclines slightly forward as it ascends, between the anterior portions 

 of the liver, to terminate in the stomach, where it is slightly con- 

 stricted. The stomach (o) is a curved oblong cavity, swelling out 

 slightly at the cardiac end, where it receives the biliary secretion, 

 continuing thence for some way of the same diameter, which is rather 

 more than half its length ; and gradually contracting to the pylorus. 

 Its tunics consist of an outer membranous, a muscular, and a smootli 

 inner mucous coat, the epithelium of which is more delicate than in 

 the cesophagus. The whole cavity is bent down at an acute angle 

 with the oesophagus, and the cardiac half is buried in the large 

 granular liver (ib. q). There is no valvular structure at the pylorus : 

 but in some specimens it presented a slight circular constriction. 

 The intestine is short, straight, and is continued downwards and a 

 little backwards, in a line with the pyloric part of the stomach to the 

 interspace between the attachments of the adductores longi and car- 

 dinales to the ventral valve, where the minute vent opens into the 

 pallial cavity. It does not perforate the capsule of the pedicle. The 

 faeces are carried out by the pallial and brachial currents.* The 

 intestine is enveloped to within a very short distance of the vent by 

 an extremely delicate venous sinus, the outer wall of which is con- 

 nected with the plicated auricles (ib. r) situated on each side of the 

 gut, a little above its middle. The muscular tunic of the intestine 



* Mr. Huxley (CCCIX. p. 108) has been unable to find this vent, and describes 

 the anal end of the intestine as imperforate. There may be blindness somewhere, 

 but I think not at the termination of the intestine of Terebratula, any more than 

 in Orhicula and Lingula. 



