

DIGESTIVE SYSTEM. 437 



towards the orifice of the shell, it will, of course, push before it the 

 wheels, so as to evert the tegumentary membrane connecting them with 

 the shell, by unrolling it like the finger of a glove, and thus causing the 

 rotatory organs to protrude at the pleasure of the animal. 



(1130.) "We have already described the means whereby the Hotifera 

 procure a supply of food, namely by exciting currents in the surround- 

 ing water ; the materials so obtained pass at once into a pharynx, the 

 relative capacity of which varies considerably in different species ; from 

 the pharyngeal receptacle it is conveyed into a singularly-constructed 

 gizzard, to be bruised and broken down by an apparatus provided for 

 that purpose ; thus prepared, it is allowed to enter a third cavity, 

 wherein digestion is accomplished, which may be called the stomach, 

 and this, after becoming gradually constricted in its diameter, terminates 

 at the caudal extremity of the body. 



(1131.) The usual arrangement of the digestive apparatus will be 

 readily understood on reference to the annexed figures : thus, in Stepha- 

 noceros EicTihornii (fig. 224), the pharynx (a) is very capacious, receiving 

 readily the materials brought into it by the ciliated arms ; the gizzard 

 (0) is a small globular viscus, containing the instruments of mastication, 

 hereafter to be noticed ; while the digestive cavity properly so called 

 (6), which presents no perceptible division into stomach and intestine, 

 extends from the gizzard to the anal aperture. 



(1132.) In Brachionus urceolaris (fig. 225) the pharynx or ossophagus 

 (e) is less capacious; the gizzard (/) exhibits through its transparent 

 coats the peculiar dental organs placed within it ; and the stomach (</) 

 is seen partially folded upon itself by the retraction of the body. We 

 observe, moreover, in this animal, appended to the commencement of 

 the stomach, two large caecal appendages (7i Ti,), which were scarcely per- 

 ceptible in the last figure, and which, no doubt, are of a glandular 

 nature, furnishing some fluid to be mixed up with the bruised aliment 

 contained in the stomach, to assist in the digestive process. To these 

 secreting caeca, Ehrenberg has chosen to give the name of pancreas ; 

 but for what reason it is diificult to conjecture, since the first rudiments 

 of a pancreas are only met with in animals far higher in the scale of 

 animal existence ; every analogy, indeed, would lead us to denominate 

 these caeca the first rudiments of a liver by far the most important and 

 universal of the glandular organs subservient to digestion, and in a 

 variety of creatures we shall afterwards find it presenting equal sim- 

 plicity of structure. In the Notommata centrura the caeca are merely 

 two pouches opening into the top of the stomach, whereas in Notommata 

 clavulata there are six of these appendages (fig. 230, e e) communicating 

 with that enlarged portion of the digestive canal (c) which may be 

 looked upon as the proper stomach. 



(1133.) We must now revert to the consideration of the dental 

 apparatus contained in the gizzard, represented in situ in fig. 225, /, and 



