58 ORGANIZATION OF THE INFUSORIA. 



referred to indifferently as the muscular or myophan layer, the latter 

 one finding most favour with Professor Haeckel. Among the types 

 in which this myophan layer is most conspicuously developed, may 

 be mentioned the genus Stentor, in which it takes the form of closely 

 set, longitudinally arranged, thread-like fibrillse ; Spirostomum, in which 

 fibrillae of similar aspect exhibit an oblique or spiral plan of disposition ; 

 and Vorticella, in which it forms a finely longitudinally striate or fibrillate 

 sheet that invests the entire body, and is continued in a condensed and 

 thread-like form down the centre of the pedicle, constituting the motile 

 or contractile element of that structure. According to the recent investi- 

 gations of Ernst Zeller, the cortical layers of the various species of Opalina 

 are found under treatment with hydrochloric acid, as shown at PL XXVI. 

 Fig. 9, to consist of closely approximated oblique or longitudinally-disposed 

 muscle-like fibrillae, though these latter by no means possess the highly con- 

 tractile properties of the myophan element as represented in the preceding 

 forms. The fourth and remaining elemental layer to be mentioned having, 

 as far as is yet known, a somewhat limited distribution, is that associated 

 with the production of the minute rod-like bodies possessing in some 

 forms an apparently urticating, and in others a simply tactile property, 

 distinguished by the name of trichocysts. The authority last quoted 

 proposes to distinguish this as a separate trichocyst layer, though whether 

 it possesses a sound claim for such distinction is at present somewhat 

 doubtful, there being forms among the Flagellata, as for example the genus 

 Raphidomonas, in which trichocysts are abundantly represented inde- 

 pendently of any specially differentiated deeper cuticular layer. The genera 

 Parameciwn, AinpJiilcptus, Prorodoii, and Nassula yield examples in which 

 these peculiar structures, described at length further on, may be most 

 advantageously examined. 



Internal Elements or Endoplasm. 



In the m.ajority of the Infusoria the central substance of the body, 

 here denominated the endoplasm, but frequently also distinguished by 

 the titles of the chyme-mass or parenchyma, — though not in this latter 

 instance to be confounded with the similarly-named element of multicel- 

 lular structures, — consists of a more or less fluid, clear or granular, but 

 otherwise undifferentiated protoplasm. This endoplasm in most instances 

 maintains a persistent or inappreciably varying status, but in a few others 

 exhibits more or less constant molecular or circulatory motions, which in 

 exceptional cases, such as Paramecium bursaria, may even assume an 

 aspect and amount of regularity analogous in many respects to the cell- 

 circulation or cyclosis of certain plants. The endoplasmic element does not, 

 however, at all times present the simple homogeneous aspect portrayed 

 in the foregoing paragraph. In a few exceptional types, such as Trache- 

 litis ovum, and Loxodes rostrum, though still more notably in Noctiluca 

 and its allies, the entire substance of the internal protoplasm is so divided 



