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the requisite changes equally in every point of 

 the body, no specific apparatus being appropri- 

 ated to the purpose. Such is the case with most 

 of the zoophytes ; and it is very remarkable, 

 that many of those which present a purse-like 

 appearance may be turned inside-out, without 

 making any material difference in their powers 

 of effecting these changes. They may be repre- 

 sented, if we please, as all stomach, or as having 

 no stomach at all ; for we may call the whole body 

 stomach, if we will, but we must at the same 

 time allow that they have no stomach, properly 

 so called. Such an animal has been defined by 

 Cuvier, a sentient self-moving sac, capable of 

 digesting food. As we ascend, however, in the 

 scale of animals, a specific organ becomes appro- 

 priated to every different function ; and hence 

 the necessity, in all but the very lowest classes, 

 of a gullet for swallowing the food ; of a stomach 

 for retaining it, till it has undergone the first step 

 of those changes to which it is to be subjected ; 

 of an intestinal canal for perfecting those changes, 

 and for transmitting it so changed to the circu- 

 lating vessels ; and of a liver, and some other 

 similar organs, for assisting, more or less essen- 

 tially, in these operations. The simplest modifi- 

 cation of a distinct digestive apparatus is to be 

 met with, among the zoophytes, in the wheel- 

 animal, in which there is a distinct membranous 

 sac for the reception of the aliment ; and a simi- 

 lar structure occurs in some kinds of sponge, in 

 the sea-blubber, and in the sea-anemone. ' In the 



