CCKLOM OF BEACHIOPODA. 311 



Alimentary Canal. 



§ 243. 



Ill tlie Bracliiopoda tlie enteric tube commences by tbe moutli, 

 wliicli is placed in tbe mantle-cavity between the two arms ; tlience, 

 and without any accessory organs, it passes, generally in the form of 

 a short canal, into the widened mid-gut (Fig. 166, d'); this is 

 generally known as the stomach. The portion which arises from 

 this passes into an enteric loop in Lingula, which turns towards the 

 right side, and opens at the anus into the mantle-cavity. This last 

 portion of the enteron is rudimentary in the Testicardines, and 

 generally terminates by a c^cal-sac which turns towards the 

 ventral valve of the shell ; from this a solid chord, which is perhaps 

 the obliterated remnant of the enteron, is sometimes continued on. 

 The end is sometimes widened out into a bulb. 



A special peculiarity in the Brachiopoda is the way in which the 

 enteron is attached. A lamella extends from the mid-gut to the 

 wall of the body ; this is the gastro -parietal band, which thus forms 

 a kind of partition in the coelom. It might be regarded as a dis- 

 sepiment, formed in connection with the already noted metamerism 

 of the body. This view of its meaning is, when we compare it with 

 the arrangements seen in the Annelides, confirmed by its relations to 

 the excretory organs. A second lamella, the ileoparietal band, is 

 similarly attached to the hind-gut. 



All the structures worthy of note which are diif erentiated from 

 the enteric wall are to be found in the mid-gut. They have the 

 form of branched tubes, which in many open into, or behind, the en- 

 largement of the enteron, already spoken of as the stomach, by several 

 pores (Crania), and in others are united into several (four) efferent 

 ducts (Lingula) . They are more largely developed in the Testicardines, 

 where they are arranged in two lateral groups of glands, wluch 

 surround the stomach, and are generally connected with it by a 

 number of ducts on either side (Fig. 166, h'). 



Ccelom and Circulatory Organs. 



§ 244. 



The coelom is divided by the organs which are embedded in it 

 and by the muscles which traverse it, into several continuous spaces 

 which are connected with the vascular system, and so form htemal 

 passages. These are also continued, as sinuses, into the lamella? of 

 the mantle, and into the arms ; in the former they break up peri- 

 pherally, and so come to be regularly arranged. The vascular 

 apparatus ramifies in these. spaces. The chief point as to their 



