746 CALKINS. [Vol. XV. 



While agreeing with Hertwig's general conception of " achro- 

 matic " structures in Protozoa, I believe that he has left out 

 of account a number of facts which have an important bearing 

 on the general problem. The " sphere " in Noctiluca is not 

 the centrosome and must be distinguished from it ; the centro- 

 some in Actinosphaeriuni (Brauer) cannot be the same as the 

 "pole-plate," and the " intra-nuclear " granule described by 

 Schaudinn in Amoeba, and the so-called " centrosome " de- 

 scribed by Balbiani must have some significance apart from the 

 "achromatic" structures which accompany them. If we take 

 these various structures into consideration, the problem becomes 

 much more complex, and the possible differentiation of sphere 

 (archoplasm) and centrosome must be sought for much earlier 

 in phylogeny. 



The most primitive nuclei in which a differentiated " achro- 

 matic " body occurs are found in Euglcna viridis and Amoeba 

 crystalligera. In both of these the nucleus consists of a nu- 

 cleolus-like body with surrounding chromatin. Keuten ('95) 

 describes this body, which up to this time had been called a 

 " nucleolus," ^ as similar to a nucleolus in its staining reactions, 

 but as playing a different role in nuclear division. He there- 

 fore calls it a " nucleolus-centrosome." 



My own observations on Etiglena viridis, and on a species of Crypto- 

 motias which has a similar central body, confirm every stage given by Keu- 

 ten, but I give a different interpretation to the staining reactions of this 

 so-calLed " nucleolus-centrosome." The color reactions which he describes 

 for this body are not those of a centrosome. It becomes " orangegelb " 

 when stained with Orange G ; with carmine solution it stains more intensely 

 than the chromatin, while with haematoxylin it takes only a faint stain. In 

 my preparations it takes a haematoxylin stain, remaining black or blue 

 when the rest of the cell is stained with Orange G. 



These reactions are characteristic of archoplasm or of the centrosphere, 

 and for this reason, if for no other, the name " nucleolus-centrosome " is 

 not entirely appropriate. Instead of comparing it with the centrosome of 

 the Metazoa, it would be much more accurate to compare it with the 

 sphere in Noctiluca or with the pole-plates of other Protozoa. A true cen- 

 trosome has not been found in it. 



1 Considerable confusion has arisen because of the indiscriminate use of the 

 term " nucleolus " in connection with protozoan nuclei. It has been applied 

 to the chromatin-masses (karyosomes) and to various " achromatic " structures. 



