ROTIFERA. 



We have already described the means whereby the Rotifera pro- 

 cure a supply of food, namely, by exciting currents in the surrounding 

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

 capacity of which would seem to vary 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 gradu- 

 ally constricted in its diameter, terminates at the caudal extremity 

 of the body. 



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

 readily understood on reference to the annexed figures ; thus, in Ste- 

 phanoceros Eichornii, (Jig- 48,) the pharynx (a) is very capacious, 

 receiving readily the materials brought into it by the ciliated 

 arms ; the gizzard (e) 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 per- 

 ceptible division into stomach and intestine, extends from the 

 gizzard to the anal aperture. 



In Brachionus urceolaris (Jig. 49) the pharynx or oesopha- 

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

 transparent coats the peculiar dental organs placed within it ; 

 and the stomach (g) 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 csecal appendages (h A), which were scarcely perceptible 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 difficult 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 cseca 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 simplicity of structure. In 

 the Notommata centrum (Jig. 50, g, #), the cseca are merely 

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

 Notommata clavulata there are six of these appendages (Jig. 



