INFUSORIAL ANIMALCULES. 75 



Tho jaws supporting the teeth, arc of a homy consistence, and arc 

 mostly furnished with two bent geniculate processes, one anterior, 

 the other posterior, in position. These processes serve for fixing the 

 jaws more firmly in situ, and, in addition, furnish powerftQ leverage 

 for the muscles working them. The jaws are further complicated 

 in some many-toothed Rotatoria — such as Philodina, Lacinulwria, 

 Melicerta, by the development of arches to support the teeth. 



The rubbing together of the opposed surfaces of the horny jaws, 

 may be readily observed, and a sort of peristaltic contraction, nearly 

 incessant, is also noticeable in the oesophageal bulb, which surrounds 

 the jaws as a muscular investment. The peristaltic contractions of 

 the bulb, led the older observers to entertain the idea that it was a 

 heart — the contractions representing its pulsations. 



The oesophageal bulb and teeth are the first perceptible organs iu 

 the embryonic Rotatoria ; and a backward and forward, or peristaltic 

 motion, may be noticed in the bulb, even before the escape of the 

 young animal from the e^^. 



In Chatonottis, this characteristic manducatory organ of the 

 Rotatoria is not distinguishable, and, most likely wanting : — for this 

 reason, as well as others, elsewhere named, Dujardin excludes this 

 genus from the order. 



Beneath the oesophageal bulb, 'the digestive tube undergoes another 

 enlargement, constituting a stomach — the connecting narrower por- 

 tion interposed between the two, being generally known as the 

 oesophagus. Mr. Goss, unfortunately, however, applies the term 

 oesophagus, to the first portion of the alimentary canal, between the 

 mouth and crop ; but the preceding application is more usual. (Des- 

 cription of Asplanchna, — Ann. Nat. Hist. 1850.) 



The oesophagus varies much in length, in difi'erent Rotatoria; 

 and very great difi'erencea are observable in the degree of develop- 

 ment of the stomach ; for, in some genera, the digestive tube con- 

 tinues as a simple, funnel-like tube, into its termination, in which 

 case, consequently, a stomach cannot be rightly said to exist, whilst, 

 in others, on the contrary, the stomach is a considerable cavity, and 

 not unfrequently sacculated. 



The canal narrows again below the stomach, forming an intestine, 

 the rectum varpng in length in diifcrent species, and ending by a 



