472 



RECENT BRACHIOPODA 



CHAP. 



ing of these cilia in Argiope ( Cistelld) when the animal is well 

 fed, and their elongation when the animal is hungry. Amongst 

 the ciliated cells certain glandular cells have been described. ■ 

 The so-called liver consists of two more or less branching glands, \^ 

 which open by wide apertures, one on each side of the stomach. 

 It seems probable that a good deal of digestion is carried on in 

 these glands, since the diatoms and other minute organisms 

 upon which the Brachiopoda live are usually found in the 

 branches of these glands, and the glandular cells lining the 

 tubules vary much in appearance according to the animal's state 

 of nutrition. 



The Body Cavity 



The alimentary canal and liver occupy a considerable por- 

 tion of the body cavity or general space 

 of the body; this space is to some ex- 

 tent cut up by the various mesenteries 

 above mentioned. It also lodges the 

 reproductive organs and the excretory 

 ducts. Its walls are ciliated, and the 

 action of the cilia keeps in motion 

 the corpusculated fluid that bathes the 

 various organs in the body cavity. The 

 mantles, which are nothing but flat- 

 tened leaf -like extensions of the body 

 wall lining the shell, also contain 

 diverticula of the body cavity, which 

 may be simple flattered spaces or may 

 be broken up into definite channels, as 

 in Lingula (Fig. 315). It seems not 

 improbable that the body cavity fluid 

 is aerated through the thin inner layer 

 of the mantle. 



Fig. 315. — \ iew of the inner side _, . , ,i i r i 



of a valve of Lingula anati- Running alono- the base ot each arm 

 /em (after Francois), to show are two canals, a small one at the base 



the definite arrangement of „ , , . , , i • i ±. 



the channels in the mantle: of the tcntaclcs, which wc may term 

 a, position of mouth; &,posi- the tentacular canal, and a larger 



tion of anus. .. i /» ,i t rr>i j? 



one, the canal ot the iip. Ine lormer 

 sends a prolongation into each tentacle. The latter is, ac- 

 cording to Blochmann, a closed canal in Crania, Lingula, Rliyn- 



