ACEPHAL.V oil LAMHLLIBHANCHIATA. 



The mouth is situated at 

 the anterior side or end ; 

 it has no teeth, but has two 

 pairs of labial tentacles. 

 The stomach, intestine, 

 and liver ara well devel- 

 oped. The heart has one 

 auricle in some cases di- 

 vided into two and one 

 ventricle, and the intestine 

 passes through it. The 

 gills or branchiae consist of 

 two pairs of delicate and 

 finely-striated t membran- 

 ous plates situated just be- 

 neath the mantle. The 

 gills not only serve for the 

 processes of respiration, 

 but by means of their vi- 

 bratile cilia they waft cur- 

 rents of water bearing food 

 to the mouth, and they 

 form a place for the hatch- 

 ing of the eggs. 



Most of the Acephals 

 effect locomotion by means 

 of the muscular " foot," 

 which in many species is 

 very large and powerful ; 

 and in the boring species, 

 as PJiolas, Teredo, etc. 

 (Figs. 632-4), it is studded 

 with siliceous particles. 

 Some kinds, as fresh-water 



Flo. f.27. 



ill 



Clam, Myn arennria. L. -The left 



valve, mantle lobe, arid half tbo 



siphons removed. 



h, heart ; m. cut-edge of the man- 

 tle ; o, .nonth : s. siphon into which 

 the water flows to bathe the gills allf l 

 to carry particles of food ; ', siphon 

 which carries the outflowing current; 

 t, labial tentacles; v, vent. 



a. a', adductor muscles; ft, body; c, 

 cloaca ; /, " foot" ; y, gills or bran- 

 chise. 



