302 Account of Professor Ehrenherg's 



in many of the higher aquatic animals, in which their purpose is 

 no ways doubtful. 



♦ The remaining external appendages of the infusoria are such 

 as are not employed as organs of motion ; they possess but little 

 interest, except as affording distinctive characters to the systema- 

 tologist. They consist of Cornicula; Cirrhi; PatellcBf or suckers, 

 which are placed at the extremity of the simple or forked tail, 

 and serve for fixing the animal ; the Proboscis or trunk, which 

 not unfrequently projects from the fore part of the head ; last- 

 ly, the Calcar or spur (Fig 1.) This last organ is a retractile 

 process, which projects from the neck in some of the Rotatoria, 

 especially the two-wheeled species. It resembles much in ap- 

 pearance the male exciting organ of the hermaphrodite mollusca ; 

 Dr Ehrenberg has, however, satisfied himself that in the infu- 

 soria, mutual impregnation by the concurrence of two indivi- 

 duals, is not necessary to the generative act, as is the case with 

 the mollusca alluded to ; and he is therefore of -opinion that 

 the organ in question must serve some different purpose which 

 has not yet been found out. 



IV. On the Alimentary (^anal of the Infusoria. 



The Digestive apparatus of the infusoria presents two princi- 

 pal forms. In the Rotatoria it consists of a simple canal, as in 

 insects ; in the Polygastrica, on the other hand, there is either a 

 canal with numerous sacs or stomachs opening into it, or several 

 stomachs unconnected by a canal. 



Again, the simple alimentary canal of the Rotatoria exists 

 under four subordinate forms (Fig. 2-6.) In the firsty it is desti- 

 tute of masticating organs, with a very long oesophagus, and a 

 simple or undivided great intestine (Fig 2.), as in the genera 

 Ichtfiydium, Chcetonottts, and Enteroplea. In the second, it is 

 furnished with masticating organs, with a very short oesopha- 

 gus, and a simple great intestine (Fig. 3.), as in Hydatina and 

 SynchcBta. In the third form, there are masticating organs, a 

 very short oesophagus, and a great intestine, divided by a con- 

 striction into an anterior or gastric portion, and a posterior por- 

 tion, or proper great intestine (Fig. 4, 5.), as in Enchlanis, Bra- 

 chicmuSy &c. Lastly, in the fourth form, there is a pharynx 

 with masticating organs, behind which the alimentary canal 



