THE NUCLEI OF UROLEPTUS MOBILIS 333 



y. COMPARISONS 



A. Multiple nuclei in ciliates 



In many ciliates a multiple number of nuclei, both macro- 

 nuclei and micronuclei, is the rule. Balbiani ('60, '61), in his 

 earlier work at least, held that the number of micronuclei is always 

 the same as the number of macronuclei, or in beaded forms, as 

 many as there are segments of the macronucleus. Maupas 

 ('83), Gruber ('87), BiitschH ('88), and many later -observers, 

 disproved this view and demonstrated that, in some cases, the 

 numbers are the same (as in the majority of Oxytrichidae) ; in 

 other cases, e.g., Trachelius ovum, Condylostoma patens, Stentor, 

 etc., the micronuclei outnumber the macronuclei; and in still 

 other cases the macronuclei outnumber the micronuclei (e.g., 

 Uronychia transfuga, Gonostomum pediculiforme, Holosticha 

 lacazei, Loxophyllum meleagris, Spirostomum ambiguum, etc.). 

 The relative numbers of the two types of nuclei, furthermore, 

 may differ in different individuals of the same species. This is 

 the case in Uroleptus mobilis, where also the number of micro- 

 nuclei is inferior to the number of macronuclei. 



a. Fusion of macronuclei during division. It is quite probable 

 that the multinucleate condition of macronuclei is only an ad- 

 vanced stage in physiological adaptation to the needs of the cell. 

 At one extreme, the more generalized condition, we find the 

 typical uninucleate cells of the majority of the infusoria. At the 

 other extreme are forms like Dileptus gigas, in which the endo- 

 plasm is filled with minute chromatin bodies each of which be- 

 haves like a granular nucleus. Between these two extremes lie 

 the ciliates with band-form, branched, beaded, or multiple 

 macronuclei. The single nucleus of Spathidium spathula is . 

 drawn out as a rod; in Euplotes, Aspidisca, Didinium, Vorticella, 

 etc., the rod becomes horseshoe shape; in many species of Suc- 

 toria it becomes much branched ; in Stentor, Spirostomum ambi- 

 guum, Bursaria, and others the rod becomes more or less con- 

 stricted at intervals to form the characteristic beaded nuclei. All 

 of these conditions are modifications of the uninucleate type. 



