NUCLEOLUS OR ENDOPLASTULE. 77 



with the associated nucleus or endoplast is maintained ; but among the 

 greater portion of the representatives of this last-named group an altogether 

 different plan of arrangement is found to obtain. The nucleolus or endo- 

 plastule is, in these, no longer immersed within the substance of the nucleus or 

 endoplast, but attached to its external periphery, or, it may be, completely 

 isolated from it. Familiar instances of such simple lateral attachment of the 

 endoplastule are afforded by the genera Paramecium, Balantidium, and 

 Nyctotherus ; this phenomenon, however, attains its most conspicuous 

 development among the Oxytrichidae and other Hypotricha, in which the 

 endoplast, as before stated, is usually represented in duplicate, and each 

 independent element accompanied by a sometimes adherent and sometimes 

 detached, minute, oval endoplastule. In Stylonychia mytilus, mostly pending 

 the process of multiplication by binary subdivision, two or even three endo- 

 plastular fragments are sometimes found associated with a single endoplastic 

 element. The most abnormal conditions and aspect of the endoplastule 

 are perhaps, however, developed in the Hypotrichous form Loxodes rostrum, 

 and in which, as shown by Wrzesniowski, the endoplastic system is repre- 

 sented by a dozen or more spheroidal elements, held in intimate union 

 with each other, but at distant intervals, by a connecting thread-like cord. 

 Within the centre of each of these spheroidal fragments a distinct central 

 endoplastule was made visible through the employment of reagents ; while, 

 in addition, a supplementary but external series of similar endoplastule-like 

 bodies was found attached, in some instances singly to the external surface 

 of the endoplast, and sometimes to the connecting cord or funiculus. In 

 that series of Infusoria including chiefly the Vorticellidae and Stentoridae, 

 in which the endoplast presents a ribbon-shaped or band-like outline, 

 the endoplastular element is mostly represented by scattered granular frag- 

 ments, one or more of which become enclosed within each of the segmental 

 portions into which the endoplast becomes separated during the process of 

 reproduction by internal gemmation, described later on. The several 

 interpretations concerning the true significance of the endoplastule, as 

 advocated by different authorities, being more fully discussed in the 

 section devoted to the reproductive manifestations of the class, it suffices to 

 add here that where this structure is developed externally to, or separate 

 from, the accompanying endoplast, recent investigation has not yielded 

 evidence in support of its fulfilling the part of a male generative organ or 

 testis, as hitherto generally supposed, but rather indicates that its nature 

 and import are essentially identical with those of the endoplast itself, and 

 whose place and functions it ultimately supplies. 



An approximate estimate of the innumerable modifications of the 

 endoplast and endoplastule of the infusorial body as now enumerated may 

 be obtained on reference to the supplementary plate (PI. XLIX.) devoted 

 especially to the illustration of these and kindred structures. 



