384 PROCEEDINGS OF THE ACADEMY OF [May, 



fundibulum, but frequently they point backward and beat in the 

 vestibuhun. The latter (Vest., figs. 20, 22, 23, 25, 27, 28) is the portion 

 of the alimentary tract placed at the base of the corona, at the junction 

 with the trunk; its lining is like that of the infundibulum. 



Attached to the narrowed posterior aperture of the vestibulum is a 

 slender tube, the oesophageal tube, (Oes.T., figs. 20, 22, 23, 25, 27, 28), 

 which extends back without posterior attachment into the proven- 

 triculus. This tube is very thin-walled, and constantly moves in rapid 

 undulations and distortions, so that its shape can be made out only 

 when it comes to rest. Nuclei could not be determined in its walls 

 in life, and all fixatives preserve it as poorly as they do the nephridia; 

 so that stained preparations did not help in understanding its structure. 

 But very delicate spirally arranged muscle fibrils compose a part of 

 its wall; and it is probable that it possesses a nerve center of its own 

 since it continues to beat after the other organs have ceased to live. 

 In a state of rest (figs. 34, 35) it is cylindrical with a posterior enlarge- 

 ment, and a very small posterior aperture into the proventriculus. It 

 is very elastic to allow the passage of large objects of food {Infusoria 

 and Mastigophora in the species studied), and may sometimes be 

 everted anteriorly into the vestibulum. 



The proventriculus (Prov., figs. 20, 22, 23, 25, 27, 28) is a large sac 

 lined by a rather thick epithelium, with readily distinguishable nuclei; 

 its internal surface is bounded by a delicate cuticula. At its posterior 

 end lies the mastax (Mast.). This consists of chitinous, jointed parts, 

 the manducatory apparatus, and of musculature for their movement. 

 Gosse (1855) holds that Stephanoceros and Floscularia have no mastax 

 in the sense that this term is used for other Rotatoria, i.e., that in the 

 Flosculariichv. it is not a special portion of the alimentary tract with a 

 lining of its own. But it is surely homologous with that of the other 

 groups, and though relatively very small I find it is not rudiment- 

 ary but possesses all the characteristic parts found in the other 

 Rotatoria. Thus in campanulata (PI. XXI, fig. 39) the manubrium 

 consists of two teeth, together constituting the uncus (Un.), and 

 of a basal piece, the manubrium (Man.). A broad chitinous plate 

 belonging also to the malleus lies below the uncus. The incus consists 

 of a median fulcrum (Fid.) and of lateral rami (Ram.). The muscula- 

 ture is difficult to determine in its exact arrangement, so that I have 

 not drawn it, but is readily seen in the living animal. The organ then 

 has a special lining, the musculature, and is truly a mastax in the sense 

 of Gosse, even though it does not form a separate compartment of the 

 alimentary tract; and this is the case also in Stejjhanoceros and Apsilus. 



