612 MlUnKh K'OIIEHTSON AND K. A. MIXruiN. 



which may be summarised as follows : (1) The centrosome 

 is to be regarded ns primnrily a body of achi-omatic^ nature, 

 elaborated and evolved, in all probability, in the nucleus 

 or in connection with it, but not itself equivalent to a 

 nucleus; (2) the centrosome is regarded as the equivalent 

 of a nucleus, and as representing primarily a nucleus which 

 has become modified and specialised both in function and 

 structure. These two theories may be termed conveniently 

 the achromatic and the nuclear theory of the centrosome 

 respectively. According to the second of these views, which 

 has recently been revived and advocated by Hai-tmann and 

 Prowazek (6), every cell is to be regarded as primarily and 

 essentially binucleate ; the two nuclei, at first, doubtless, 

 equivalent and similar in all respects, became modified in two 

 directions respectively, the one becoming specialised for 

 trophic, the other for kinetic functions, with coiresponding 

 differentiation of structure. In the metazoan cell, according 

 to this theory, the nucleus represents the original trophic 

 nucleus deprived of all kinetic structures, while the centro- 

 some represents the kinetic nucleus deprived of all " vegeta- 

 tive " functions and of its chromatic apparatus. On this 

 interpretation of the centrosome, the minute granules which 

 are the centre of kinetic functions are termed "centrioles," in 

 order to distinguish them from the centrosomes as a whole. 

 In fact, from the point of view of the nuclear theory of the 

 centrosome, the centriole requires to be defined in exactly the 

 same waj' as the centrosome itself on the achromatic theory. 



The confusion produced by these two theories of the cen- 

 trosome reaches its height in the nomenclature of the different 

 parts of the body of a trypanosome. In these organisms, and 

 in allied genera of flagellates, there are three distincts parts 

 of the nuclear apparatus to be reckoned with. First, there 



^ Meaniug by tlie term '" achromatic " something which is not com- 

 posed of chromatin, not necessarily something -which is not coloiired 

 by stains. All is not chromatin that stains, even with a so-called 

 nuclear stain. In our opinion a great deal of error and misconception 

 has arisen by identifying as '" chromatin " all bodies in the cell that are 

 coloured black, for instance, by the iron-hseniatoxylin method. 



