76 ORGANIZATION OF THE INFUSORIA. 



species of Opalina, as recently demonstrated by Engelmann and Ernst 

 Zeller, the number of endoplastic elements almost exceeds computation, and 

 takes the form of exceedingly minute spheroidal corpuscles associated with 

 a central endoplastule distributed everywhere throughout the substance of 

 the cortex. It is almost needless to remark that in each of these com- 

 pound phases the infusorial endoplast differs essentially from the ordinary 

 tissue nucleus, which is there invariably represented in its simple and 

 single form. By those who contest the unicellular organization of the 

 Infusoria, this frequent occurrence of a multiplicity of endoplastic elements 

 has, as previously observed, been referred to as yielding the strongest 

 evidence of multicellular structure. Such testimony is, however, entirely 

 neutralized when correlated with the fact that this element has to be 

 regarded as differing essentially in a variety of aspects from the nucleus 

 of the simple histologic cell, one of the more important of these being 

 its capacity to multiply indefinitely within, and independently of, the 

 circumambient cell-wall or its equivalent. In connection with this phenome- 

 non, and as more fully explained in the section devoted to the reproduc- 

 tive features of the class, the infusorial endoplast, in both its attenuate 

 band-like, and compound aspect, has to be regarded in the light of a 

 specialized proliferous stolon, adapted for the production under certain con- 

 ditions of a greater or less number of embryonic zooids, and as a supplement 

 to that more normal mode of increase by duplicative division or fission 

 which resembles the only reproductive faculty possessed by the ordinary 

 tissue-cell. One feature of importance presented by the infusorial endoplast 

 remains to be enumerated. In accordance with the results of the most recent 

 investigation, and in connection with which the names of Greeff and Biitschli 

 have especially to be mentioned, it has been demonstrated beyond question 

 that in its more complex form this structure is enclosed within a delicate 

 and hyaline bounding membrane or pellicle, which may, perhaps, be most 

 appropriately compared, physiologically and so far as its structureless 

 nature is concerned, with the similarly transparent and structureless pellicle 

 ensheathing the constituent elements of ordinary muscular tissue, known 

 as the " sarcolemma." It is apparently of this hyaline supplemental 

 envelope alone that the slender and transparent filamentous cords, or 

 funiculi, are composed that hold in union with one another the otherwise 

 disjointed fragments of the compound endoplast, as represented in the 

 genera Loxodes and Loxophyllum. 



That marked disparity of aspect and significance recorded of the infu- 

 sorial endoplast, as compared with the ordinary histologic nucleus, is found 

 to extend likewise to the nucleolus or endoplastule. In all ordinary tissue- 

 cells this special structure is found to constitute an integral and essential 

 constituent of the nucleus, of which organ it presents the appearance 

 merely of a central, more solid, and opaque spheroidal fragment. With the 

 majority of the Flagellata and some few Ciliata, such as Pleiironema and its 

 allies, and many of the Chilodontidae, a similar contour and relationship 



