INTERNAL (ECONOMY. 415 



tentaculum do not, as has been sometimes stated, give 

 an impulse in opposite directions; but both strike 

 downwards, and towards the mesial line of the ten- 

 taculum to which they are attached, causing a current 

 down the centre of its internal surface, whereby the 

 particles of carmine are carried towards the mouth. 

 At this part all the streams converge, and thus give 

 rise to an upward central current, by which the par- 

 ticles of carmine are carried outwards. None of the 

 carmine seems to enter the oesophagus, although the 

 particles will sometimes be found collected in con- 

 siderable quantities around the mouth, before they 

 are floated away, a circumstance, which would indi- 

 cate that these little creatures possess the power of 

 selecting such substances only as are adapted to their 

 nourishment. 



The tentacula are united together at their base so 

 as to form a circle, in the centre of which is situated 

 the mouth, from whence is prolonged a capacious and 

 highly irritable oesophagus that contracts vigorously 

 when food is introduced into it. To the oesophageal 

 tube there succeeds in some species (Bowerbankia*) 

 a contractile gizzard, the walls of which are lined 

 with a wonderfully-constructed pavement of tessel- 

 lated teeth, by the aid whereof the aliment is crushed 

 and bruised preparatory to its admission into the 

 proper digestive stomach, whence an intestinal canal 



* The BOWERBANKIA DENSA is commonly found on Flustra 

 foliacea, thickly aggregated in patches of half an inch to one 

 inch in diameter ; and will be easily procured by the indus- 

 trious microscopist who wishes to enjoy the luxury of exa- 

 mining it. 



