CONCHIFEKA. 



217 



vermiform; it can be protruded or withdrawn, and in 

 solitary cases may be used for creeping. The byssus is 

 much diversified ; in the Area it is a single compact body ; 

 in the Pinna it consists of threads separate in their whole 

 length, and so fine as to be manufactured into cloth called 

 Lama marina. 



The mouth is situated near the back of the animal, within 

 the cavity of the mantle ; it has no jaws, but is provided 

 on each side with two, lobed, often sickle-shaped tentacles, 

 which frequently in their structure look like gills. The 

 oesophagus is short, leading into a crop-like distension, but 

 it is not otherwise separated from the intestinal canal. 

 Many conchifera have a kind of blind sac rising near the 

 pylorus, which through its whole length contains a cartila- 

 ginous, glassy cylindrical body, the so-called " crystalline 

 stylet." This is a kind of gizzard for triturating the 

 food. 



Their nutriment, consisting of slime and small organised 

 bodies, is taken up with a portion of water into the cavity 

 of the mantle, and by means of the shining epithelium or 

 horny lining of the mantle, is directed towards the mouth, 

 assisted by the before-mentioned lip tentacles. 



All conchifera have a large liver, which occupies a con 

 siderable portion of the back, also a well developed heart, 

 with colourless blood. There are usually two pair of gills, 

 which enfold the body on either side like two leaves, and 



! have a network of canals, along which the blood streams. 

 In the Area, Peetunculus, JPecten, and Spondylus, the 



: gills are broken up into a multitude of ribbon-like filaments, 

 lying in rows close to one another, and in the Solenomya 

 they look like down. The water reaches them through the 

 mantle slit, or, where this is closed up, through a par- 

 ticular aperture, and is afterwards discharged, For the 

 latter purpose the mantle, when it is not slit, has at 



