70 6ENEBAI HI8T0EY OF 



several eliding segmonts. Very fine muscular threads ore likewise 

 employed to keep the viscera ia their places; and some transverse 

 ones crossing the general ca\'ity of the body, have, in some instances, 

 been seen. (Plate XXIII, fig. 5.) 



Mr. Gosse says: "AU the cuticular insertions (of the muscles) 

 are in a skin separable from the outer integument. . . . The coronet 

 of thickened masses that surround the head is probably muscular, 

 bearing the cilia. Just below this (in Asplancha priodontn) there is a 

 series of five or six annular threads, set in the inner skin, which are 

 probably muscular, and aid in the complex movements of the head. 

 The reniform cushion that bears the jaws, is, doubtless, composed of 

 powerful muscles ; and the delicate stomach with its tube, the great 

 crop and the ovisac, are covered with a muscular network." 



The muscles of the Rotatoria have a clear, distinct outline, but 

 are not transversely striated, and belong to the imstriated muscular 

 tissue of anatomists. 



Dujardin (Histoire des Infusoires, p. 557) is the only recent 

 writer w© have met with, who denies the existence of distinct 

 muscles in this class. He would attribute the movements witnessed, 

 to the operation of a soft, diaphanotis, diffluent substance, subjacent 

 to the integument, which he further supposes to possess an inherent 

 property of contractility. This same author excludes the genus 

 ChcBtonotus from the Rotatoria, under the impression that it does not 

 present the characteristic contractility of the class, and, above aU, 

 that it has no true rotary organ. 



The most singular and interesting organ in these creatures, if not 

 the most remarkable structure in the animal kingdom, is the so-called 

 rotary or rotatory organ ; it consists essentially of a whorl of cilia, 

 seated on a contractile base, forming the head of the animals. It 

 constitutes the piincipal means of locomotion, the tail process being, 

 in most cases, less concerned. Even where the animal, by the alter- 

 nate fixing of its mouth and tail, can progress like a leech, it can, 

 also, more rapidly advance by the propulsion of its ciliated wheel 

 apparatus. 



The rotary movement of this apparatus was, at one time, looked 

 upon as a reality, but is now regarded as only ajiparent. Dutrochet 

 attributed the phenomenon to the undulation of a delicate membrane 



