394 CALKINS. 



in the other it is intra-nuclear (Euflagellata). The significance 

 of the central granule as an attraction-center in the case of Eii- 

 glejia was early recognized by Biitschli ('87), Blockmann ('94), 

 Keuten ('95), Lauterborn ('95) and others who saw in it a prim- 

 itive centrosome. Hertwig more recently ('96) accepted the 

 idea and explained the central body in Euglena, together with 

 the large spheres in Noctiluca and the pole-plates found in various 

 Protozoa as centrosomes of the type observed by himself in sea- 

 urchin eggs after treatment with various salts. I have shown 

 above, however, that the sphere in Noctiluca^ the cytoplasmic 

 body of Tctramitiis, the Ncbcnkorpcr of Parainceba and the in- 

 tra-nuclear body of CJiilomoiias, Euglcna and allied forms are an- 

 alogous structures and that they have the same physiological 

 function to play in the activity of the cell. But it has also been 

 shown that there is a true centrosome in the sphere of Noctiluca. 

 The intra-nuclear body of Rjiglena therefore cannot be called a 

 centrosome as the above-named observers have designated it, 

 and cannot be compared with the centrosome of the Metazoa. 

 It is comparable however with the cytoplasmic bodies of Para- 

 nioeba, of Noctiluca, and therefore with the attraction -sphere of 

 metazoan nuclei. Moreover, this element seems to arise in the 

 simplest cases as a cytoplasmic structure and independently of 

 chromatin or nucleus (Tctraniitus). It appears therefore that 

 Boveri's original conception of an independent cellular substance, 

 the archoplasm, holds good in the case of the Protozoa. By 

 considering the intra- or extra-nuclear body of Protozoa as 

 archoplasm in the form of an attraction sphere, rather than as a 

 centrosome, the various conflicting views in regard to these 

 structures can be more or less brought together. By this view 

 can be explained the origin and significance of the central spindle 

 of the Metazoa (cf. Ccntrodcsuius of Heidenhain) ; the origin of 

 spindles without centrosomes in the higher plants (cf. Stras- 

 burger's Kinoplasmd) ; and, to some extent, the various inter- 

 pretations of the function, origin and fate of the centrosome. 

 According to this view the centrosome is originally of minor 

 importance, the sphere alone being functional as an attraction 

 center. The centrosome appears to be of later origin, although 



